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The biological and clinical significance of the p.E88del variant in the transcobalamin receptor, CD320, is unknown. This allele is annotated in ClinVar as likely benign, pathogenic, and of uncertain significance. To determine functional consequence and clinical relevance of this allele, we employed cell culture and genetic association studies. Fibroblasts from sixteen CD320 p.E88del homozygotes exhibited reduced binding and uptake of cobalamin. Complete ascertainment of newborns with transiently elevated C3 (propionylcarnitine) in New York State demonstrated that homozygosity for CD320 p.E88del was over-represented (7/348, p

Gaucher disease (GD), one of the most common lysosomal disorders, is caused by deficiency of β-glucocerebrosidase. Based on the presence and severity of neurological complications, GD is classified into types I, II (the most severe form), and III. Abnormalities in systemic markers of vitamin B12 (B12 ) metabolism have been reported in GD type I patients, suggesting a higher prevalence of B12 deficiency in these patients. A 2-month-old male with GD type II was admitted to the hospital presenting jaundice, hepatosplenomegaly, and ichthyosis. At admission, cholestasis and ascites, abnormal liver function enzymes, prolonged prothrombin time, and high levels of B12 were confirmed. Analysis of biomarkers of B12 status revealed elevated B12 and holo-transcobalamin (holo-TC) levels. The B12 profile found in our patient is the opposite to what is described for GD type I patients. Holo-TC may increase in inflammatory states or due to liver diseases. In GD, the accumulation of glucocerebroside may be a trigger that initiates a systemic inflammatory reaction, characterized by macrophage activation. We suggest higher levels of holo-TC could be associated with a more severe (neuronopathic) GD, and be a biomarker of GD type II.

Colorectal cancer (CRC) is characterized by DNA methylation, which is associated with genomic instability and tumor initiation. As an important epigenetic regulation, DNA methylation can be used as a potential therapeutic target for CRC. In our study, we downloaded DNA methylation profiles (GSE17648 and GSE29490) and RNA sequencing microarray data (GSE25070 and GSE32323) from the Gene Expression Omnibus (GEO) database. As a result, 14 aberrantly methylated differentially expressed genes (DEGs) were screened according to the different criteria. We further validated these DEGs in The Cancer Genome Atlas (TCGA) database and obtained Pearson's correlation coefficient (COR) for the relationship between gene expression and DNA methylation. Three candidate genes (SOX9, TCN1, and TGFBI) with COR greater than 0.3 were screened out as Hub genes. The receiver operating characteristic result indicated that SOX9 and TGFBI effectively serve as biomarkers for the early diagnosis of CRC. Furthermore, the potential prognosis of the Hub genes for CRC patients was evaluated. Only TGFBI, which is regulated by methylation, can predict patient disease-free survival. Additionally, we examined the methylation level of the Hub genes in CRC cells in the Cancer Cell Line Encyclopedia database. Considering that methylation status tends to be highly modified on CpG islands in tumorigenesis, we screened the CpG island methylation of TGFBI based on the TCGA database and verified its diagnostic value in the GEO database. Our result revealed two Hub genes (TCN1 and TGFBI) whose aberrant expressions were regulated by DNA methylation. Additionally, we uncovered the hypermethylation of TGFBI on CpG islands and its clinical value in the diagnosis of CRC.

Background Reducing meat consumption is often advised; however, inadvertent nutritional deficiencies during pregnancy may result in residual neurodevelopmental harms to offspring. This study assessed possible effects of maternal diets in pregnancy on adverse substance use among adolescent offspring. Methods Pregnant women and their 13-year-old offspring taking part in a prospective birth cohort study, the Avon Longitudinal Study of Parents and Children (ALSPAC), provided Food Frequency Questionnaire data from which dietary patterns were derived using principal components analysis. Multivariable logistic regression models including potential confounders evaluated adverse alcohol, cannabis, and tobacco use of the children at 15 years of age. Results Lower maternal meat consumption was associated with greater problematic substance use among 15-year-old offspring in dose–response patterns. Comparing never to daily meat consumption after adjustment, risks were greater for all categories of problem substance use: alcohol, odds ratio OR = 1.75, 95% CI = (1.23, 2.56), p

BACKGROUND The clinical use of holotranscobalamin (holoTC) testing to evaluate vitamin B12 status has increased in recent years. We present two patients (African Caribbean and Indian heritage), in which the holoTC assay indicated severe B12 deficiency (< 5 pmol/L). Additional clinical tests revealed that these patients had normal levels of total vitamin B12 in blood and unremarkable levels of two other markers of vitamin B12 status, homocysteine and methylmalonic acid. We hypothesized that these patients carry a variant in the transcobalamin gene (TCN2) that influences the most widely commercially available holoTC test - Active-B12 (Axis-Shield Diagnostics Ltd). DESIGN Exon sequencing of the TCN2 gene was carried out. Protein characterization included total transcobalamin (TCN2) detection by Western blot, and holoTC by (57) Co-labelled B12 binding followed by size fractionation. RESULTS Exon sequencing of TCN2 revealed both patients were homozygous for the minor allele of rs35838082 (p.R215W). Western blot and chromatographic analyses revealed that the serum of these patients contains intact transcobalamin and that this variant-containing protein binds vitamin B12 . The variant is rare in Caucasians (minor allele frequency (MAF) < 0·01) but more common in South Asians (MAF ~ 0·02) and those of African origin (MAF ~ 0·25). CONCLUSIONS The impeded ability to detect normal levels of holoTC in these two patients may be due to this variant interfering with the detection of holoTC by one or both of the monoclonal antibodies currently employed in the Active-B12 test. Laboratories should be aware of this variant and use confirmatory tests when applicable.

Transcobalamin (TC) transports cobalamin from blood into cells. TC deficiency is a rare autosomal recessive disorder usually presenting in early infancy with failure to thrive, weakness, diarrhoea, pallor, anemia, and pancytopenia or agammaglobulinemia. It can sometimes resemble neonatal leukemia or severe combined immunodeficiency disease. Diagnosis of TC deficiency is suspected based on megaloblastic anemia, elevation of total plasma homocysteine, and blood or urine methylmalonic acid. It is confirmed by studying the synthesis of TC in cultured fibroblasts, or by molecular analysis of the TCN2 gene. TC deficiency is treatable with supplemental cobalamin, but the optimal type, route and frequency of cobalamin administration and long term patient outcomes are unknown. Here we present a series of 30 patients with TC deficiency, including an update on multiple previously published patients, in order to evaluate the different treatment strategies and provide information about long term outcome. Based on the data presented, current practice appears to favour treatment of individuals with TC deficiency by intramuscular injections of hydroxy- or cyanocobalamin. In most cases presented, at least weekly injections (1 mg IM) were necessary to ensure optimal treatment. Most centres adjusted the treatment regimen based on monitoring CBC, total plasma homocysteine, plasma and urine methylmalonic acid, as well as, clinical status. Finally, continuing IM treatment into adulthood appears to be beneficial.

The membrane receptor TCblR/CD320 binds transcobalamin (TC) saturated with vitamin B12 [cobalamin (Cbl)] and mediates cellular uptake of the vitamin. The specificity of TC for Cbl and of the receptor for TC-Cbl ensures efficient uptake of Cbl into cells. The high-affinity interaction of TCblR with TC-Cbl (Ka=10 nM−1) was investigated using deletions and mutations of amino acid sequences in TCblR. Only the extracellular region (aa 32–229) is needed for TC-Cbl binding, but the N-glycosylation sites (N126, N195, and N213) are of no importance for this function. Deleting the cysteine-rich region (aa 95–141) that separates the two low-density lipoprotein receptor type A (LDLR-A) domains does not affect TC-Cbl binding (Ka = 19–24 nM−1). The two LDLR-A domains (aa 54–89 and 132–167) with the negatively charged acidic residues involved in Ca2+ binding are critical determinants of ligand binding. The cytoplasmic tail is apparently crucial for internalization of the ligand. Within this region, the RPLGLL motif and the PDZ binding motifs (QERL/KESL) appear to be involved in initiating and completing the process of ligand internalization. Mutations and deletions of these regions involved in binding and internalization of TC-Cbl are likely to produce the biochemical and clinical phenotype of Cbl deficiency.—Jiang, W., Nakayama, Y., Sequeira, J. M., Quadros, E. V. Mapping the functional domains of TCblR/CD320, the receptor for cellular uptake of transcobalamin-bound cobalamin.

Background Vitamin B12 and homocysteine have been shown to be associated with depression or depressive symptoms, but the relationship has not been universal. Both vitamin B12 and homocysteine may exert an effect via vascular mechanisms; it is possible that other mechanisms apply. Holotranscobalamin is a novel, more accurate measure of tissue vitamin B12. Objectives To examine associations between vitamin B12, serum folate, holotranscobalamin, homocysteine and depressive symptoms in a sample of healthy elderly. Methods Cross-sectional, observational community based study. Results Lower levels of holotranscobalamin and vitamin B12 were associated with higher levels of depressive symptoms when controlled for Mini-mental state examination scores and psychosocial and cardiovascular risk factors. Homocysteine was not associated with depressive symptoms when biological and psychosocial covariates were included. Conclusions It is possible that low levels of vitamin B12 or holotranscobalamin are associated with depressive symptoms via mechanisms other than vascular pathology. Copyright © 2010 John Wiley & Sons, Ltd.

The sources and biochemical characteristics of cobalamin-binders in amniotic fluid were investigated. Using gel-permeation chromatography, cobalamin-binder, extracted from amniotic fluid at term, was recovered in a single peak with the molecular size of haptocorrin. Neonatal saliva also contained only haptocorrin. However, neonatal gastric juice contained two types of cobalamin-binders: haptocorrin and intrinsic factor. Amniotic fluid in midtrimester contained three types of cobalamin-binders: haptocorrin, intrinsic factor, and transcobalamin II. The cultured amnion cells secreted mainly apo-transcobalamin II. Concentrations of both apo-haptocorrin and salivary amylase in amniotic fluid increased as gestation advanced. These results suggest that cobalamin-binder in amniotic fluid in midtrimester originates from the fetal salivary gland, fetal gastric mucosa, and amnion cells, and that the contribution by the fetal salivary gland increases at term, when almost all cobalamin-binders in amniotic fluid are haptocorrin.

International audience; Transcobalamin (transcobalamin II, TC) transports plasma vitamin B(12) (cobalamin, Cbl) into cells. TC deficiency is a rare autosomal recessive disorder causing intracellular Cbl depletion, which in turn causes megaloblastic bone marrow failure, accumulation of homocysteine and methylmalonic acid, and methionine depletion. The clinical presentation reflects intracellular Cbl defects, with early-onset failure to thrive with gastrointestinal symptoms, pancytopenia, and megaloblastic anemia, sometimes followed by neurological complications. We report the clinical, biological, and molecular findings and the outcome in five TC-deficient patients. The three treated early had an initial favorable outcome, whereas the two treated inadequately had late-onset severe neuro-ophthalmological impairment. Even if the natural course of the disease over time might also result in late-onset symptoms in the aggressively treated patients, these data emphasize that TC deficiency is a severe disorder requiring early detection and probably long-term aggressive therapy. Mutation analysis revealed six unreported mutations in the TCN2 gene. In silico structural analysis showed that these mutations disrupt the Cbl-TC interaction domain and/or the putative transcobalamin-transcobalamin receptor interaction domain.

The third-generation peptide-dendrimer B1 (AcES)8(BEA)4(K-Amb-Y)2BCD-NH2 (B=branching (S)-2,3-diaminopropanoic acid, K=branching lysine, Amb=4-aminomethyl-benzoic acid) is the first synthetic model for cobalamin-binding proteins and binds cobalamin strongly (K(a)=5.0 x 10(6) M(-1)) and rapidly (k(2)=346 M(-1) s(-1)) by coordination of cobalt to the cysteine residue at the dendrimer core. A structure-activity relationship study is reported concerning the role of negative charges in binding. Substituting glutamates (E) for glutamines (Q) in the outer branches of B1 to form N3 (AcQS)8(BQA)4(B-Amb-Y)(2)BCD-NH2 leads to stronger (K(a)=12.0 x 10(6) M(-1)) but slower (k(2)=67 M(-1) s(-1)) cobalamin binding. CD and FTIR spectra show that the dendrimers and their cobalamin complexes exist as random-coil structures without aggregation in solution. The hydrodynamic radii of the dendrimers determined by diffusion NMR either remains constant or slightly decreases upon binding to cobalamin; this indicates the formation of compact, presumably hydrophobically collapsed complexes.

Transcobalamin (TC) I deficiency, like the function of TC I itself, is incompletely understood. It produces low serum cobalamin levels indistinguishable from those of true cobalamin deficiency. Diagnosis is especially elusive when TC I deficiency is mild. To provide new, more substantive definition, the TCN1 gene was examined in two well-characterised families that included members with both severe and mild TC I deficiencies. A severely deficient proposita with undetectable TC I levels displayed compound heterozygosity for two mutations, each causing a premature stop codon. Relatives in both families who had mildly low or low-normal plasma levels of TC I and cobalamin were heterozygous for one or the other of these mutations. An unrelated patient with mild TC I deficiency and unknown familial TC I and cobalamin status was then tested and found to be similarly heterozygous for one of the mutations. The two nonprivate mutations identify a genetic basis for TC I deficiency for the first time. They also add new approaches to studying mild and severe TC I deficiency and to reducing confusion of its low cobalamin levels with those of cobalamin deficiency and its often dramatically different prognosis and management.

Cobalamin (vitamin B(12)) is an essential cofactor in a variety of enzymatic reactions and most prokaryotes contain transport systems to import vitamin B(12). A gene coding for a periplasmic cobalamin-binding protein of Photobacterium damselae subsp. piscicida was identified by in silico analysis of sequences from a genomic library. The open reading frame was composed of 834 bp encoding a protein of 277 amino acids. The protein showed 61% identity with the vitamin B(12)-binding protein precursor of P. profundum, 53% identity with the corresponding protein of Vibrio parahaemolyticus and 43% identity with the periplasmic binding protein BtuF of Escherichia coli. The expression of the native protein was investigated in P. damselae subsp. piscicida, but BtuF was weakly expressed under normal conditions. To characterize the BtuF of P. damselae subsp. piscicida, the recombinant protein was expressed with a C-terminal His(6)-tag and purified; the molecular weight was estimated to be approximately 30 kDa. The protein does not contain any free thiol group, consistent with the view that the two cysteine residues are involved in a disulphide bond. The purified BtuF binds cyanocobalamin with an affinity constant of 6 +/- 2 microm.

The unsaturated vitamin B12 binding capacity (UBBC) of serum, the three transcobalamins (TC I, TC II, TC III), and the total leucocyte and neutrophil counts have been studied in paediatric patients with sickle cell disease (SCD). Increase in the level of the binding capacities of TC I and TC II with concomitant increase of UBBC was observed in these children who also had increased total white blood and neutrophil counts. There was a significant reduction in the level of endogenous B12. These abnormalities are discussed in relation to the deficiency of the splenic reticuloendothelial function, immunologic defect, hepatic degenerative changes and aplastic crisis observed in SCD. These results lend support to the view that transcobalamins are involved in the defence mechanism of the body. The significant reduction in serum cobalamin in SCD suggests a higher demand on this vitamin for metabolic functions, especially for the sparing of folate.

Unsaturated plasma transcobalamin II (UTC II) and cobalamin were measured in two selected age-groups of like-sexed mono- and dizygotic twins. For UTC II, a higher mean level was found in women than in men, and in the older (57 to 61 years) than in the younger (33 to 39 years) age group. Testing of genetic-environmental models revealed that variation in plasma levels of UTC II is almost exclusively genetically determined. More than 50% of the variation in cobalamin levels was accounted for by genes, the remainder being due to person-specific environmental factors (for older males no model gave a good fit). A negative correlation was noted between UTC II and cobalamin levels. The correlation coefficient was low, and the variation in UTC II accounted for only about 4% of the variation in the cobalamin level. This finding suggests that a pathologically high value of one of the variables may have clinical significance, regardless of the value of the other variable. For 22 patients studied longitudinally, a clear tendency to maintain plasma levels at constant levels over long periods of time was found, suggesting that certain degrees of deviation from these levels may have clinical relevance.

P-Cobalamins have been reported to be decreased in patients with HIV infection. Because of this, we found it of interest to examine both cobalamin-saturated binding proteins (holo-transcobalamin, holo-TC and holo-haptocorrin, holo-HC) and cobalamin unsaturated binding proteins (apo-transcobalamin, apo-TC and apo-haptocorrin, apo-HC). The results are given as range and (median). Eighteen male HIV-infected patients with plasma cobalamins below 200 pmol/l were studied. We found low concentrations of holo-TC (37-88 (47.5) pmol/l) and holo-HC (64-184 (135.5) pmol/l). The concentration of apo-TC and apo-HC was increased (480-1730 (1025) pmol/l; 70-800 (235) pmol/l). It is concluded that, in HIV-infected patients, low plasma cobalamin does not reflect a low concentration of transcobalamin or haptocorrin. In 20 HIV-infected patients and 31 patients with malignant haematological diseases, the TC isopeptide patterns were determined. In the HIV group, an increased frequency of TC isopeptide X was found and the overall distribution of TC isopeptides was significantly different from the reference population (p less than 0.05). There was no difference between the group of patients with malignant haematological diseases and the reference group.

A patient with hepatocellular carcinoma, megaloblastic anaemia and increased concentration of serum cobalamin is described. Plasma TC I was increased to 10,000 times the normal concentration, thus explaining the increased concentration of serum cobalamin and a false Schilling test. The increase in plasma TC I in concurrence with undetectable amounts of plasma TC II was a likely explanation for the anaemia. The electron microscopic picture of the hepatocellular carcinoma was in accordance with TC I being produced by the tumour cells.

A patient with metastatic carcinoma of the breast and increased plasma cobalamin binding capacity (about 50 nmol/1) is described. The binding protein was identified as transcobalamin I (TCI) by DEAE cellulose ion-exchange chromatography, Sephadex G200 gel filtration and agar gel electrophoresis. Although the total plasma cobalamin concentration (about 20 nmol/1) was elevated, the patient complained of neurological symptoms in accordance with a functional vitamin B12 deficiency. Hence, an inactivation of the coenzyme is suggested by the demonstration of considerable amounts of 5′-deoxyadenosylcobalamin bound to the plasma TCI. Both urinary excretion of FIGLU and methylmalonic acid were within the reference ranges. Reported cases of increased cobalamin binding in patients with nonhaematological malignancy are reviewed. Further investigations to characterize the function of the cobalamin dependent metabolic pathways are necessary to determine the importance of the increased transcobalamin binding in these patients.

A 38-year-old woman developed chronic myeloid leukaemia after 2 years of lithium carbonate therapy. A peculiar feature of her leukaemia, as well as of the 5 patients previously reported in whom CML has developed in the course of lithium therapy, was the unusually high degree of granulocyte maturation manifested in normal leucocyte alkaline phosphatase (LAP) score and, in 1 case, selective increase of transcobalamin III. Although a cause and effect relation between lithium therapy and CML has not yet been established, in view of the stimulatory effect of lithium on granulocyte proliferation, such treatment should be avoided in patients with established myeloproliferative disorders, or in patients at high risk of developing leukaemia.

Oral routes of administration for therapeutic peptides and proteins face two major barriers: proteolytic degradation in the stomach and an inadequate absorption mechanism for polypeptides within the intestinal lumen. As a result, peptide-based therapeutics are administered by injection, a painful process associated with lower patient compliance. The development of a means of overcoming these two major obstacles and enabling the successful delivery of peptide therapeutics by the oral route of administration has therefore been the target of extensive scientific endeavor. This Minireview focuses on oral peptide/ protein delivery by the dietary uptake pathway for vitamin B 12. Recent progress in this field includes the delivery of erythropoietin, granulocyte-colony-stimulating factor, luteinizing-hormone- releasing hormone, and insulin.

It is unusual for inborn errors of metabolism to be considered in the investigative work-up of pancytopenia. We report a family in which the proband presented with failure to thrive at 2 months of age and subsequent bone marrow failure. A previous sibling had died at 7 months of age with suspected leukaemia. Haematological findings in the proband were significant for pancytopenia, and bone marrow aspiration showed dysplastic changes in all cell lineages. Urinary organic acid analysis revealed elevated methylmalonic acid. The synthesis of transcobalamin II (transcobalamin, TC) by cultured fibroblasts was markedly reduced, confirming the diagnosis of TC deficiency. The proband and his younger asymptomatic sister (also found to have TC deficiency) were homozygous for R399X (c.1195CT), a novel mutation resulting in the loss of the C- terminal 29 amino acids of TC, a highly conserved region. Response to parenteral vitamin B(12) in the proband was dramatic. At 6 years 3 months of age, physical examination is normal and developmental level is age appropriate. His sister is clinically asymptomatic and is also developing normally. Propionylcarnitine concentrations were not elevated in the newborn screening cards from the proband and sister, but that was for specimens retrieved from storage after 7 years and 5 years, respectively. Inherited and acquired cobalamin disorders should both be considered in the differential diagnosis of bone marrow failure syndromes in young children. Early detection of the metabolic causes of bone marrow failure can ensure prompt recovery in some cases involving the vitamin B(12) pathway.

The genetic locus of human transcobalamin II (TC2) is not yet known. The mouse transcobalamin II gene has been assigned to mouse chromosome 11, linked to hemoglobin A. This fact suggested a similar linkage of transcobalamin II in man, assigning it thus to human chromosome 16. Our linkage investigation in a family material of more than 600 individuals demonstrated absence of linkage between transcobalamin II and phosphoglycolate phosphatase, which is very closely linked to hemoglobin A on chromosome 16. Additionally we confirmed absence of linkage with the chromosome 16 gene marker system haptoglobin. These two gene marker systems are located far from each other, and the total length of chromosome 16 is estimated only about 100 cM. Together with recent results of investigations in somatic mouse-man cell hybrids, we conclude that TC2 is not located on chromosome 16. Additionally we found absence of linkage between transcobalamin II and 6-phosphoglucona-te dehydrogenase, rhesus blood group (both on chromosome 1), GC (chromosome 4), Esterase D (chromosome 13) and AG; absence of close linkage with “debrisoquin polymorphism”.

Natural proteins acquire their function by organized folding, which leads to the formation of active sites. Many proteins incorporate cofactors to complement their functionality. In the case of metal-containing cofactors such as porphyrins or cobalamins, the protein acts as a protecting shell around the cofactor; this leads to altered reactivity at the metal center. While porphyrin-containing proteins have been studied in a number of synthetic model systems, no synthetic macromolecules have been reported that mimic the cobalt binding in B12-dependent enzymes or transport proteins. In a recent study, a monoclonal antibody against coenzyme B12 was reported that reconstitutes the “base-on” form of B12 coenzymes without direct coordination to the metal center. A similar binding mode was reported in a selected aptamer ligand for cyanocobalamin. Herein, we explored the molecular principles of cobalamin–peptidic ligand interaction with libraries of peptide dendrimers. Recognition and discrimination among a large number of amino acid sequences led to a peptide dendrimer model for a cobalamin-transport protein. In our peptidic ligands, cofactor binding is mediated by a coordinating cysteine or histidine residue at the dendrimer core and is assisted by secondary interactions in the dendritic shells. Dendrimers are branched macromolecules that can adopt a globular or disk-shaped structure that is well suited to create synthetic models of proteins. We recently reported peptide dendrimers that consist of natural amino acids arranged in a tree-like dendrimer topology by using a branching diamino acid at every second, third or fourth position in the peptide sequence. These dendrimers display catalytic, lectin binding and drug-delivery activities. While these functions resulted from multivalency effects of functional groups in the dendritic branches, the dendritic structure should also be well suited to engage in binding interactions at the dendritic core, which might form a tight complex in which a ligand could be secluded from solution by the surrounding dendritic branches, as was observed with porphyrins that had been functionalized with dendritic branches. To test this hypothesis, we investigated binding to aquocobalamin, for which we had already discovered multivalent but only weakly coordinating dendritic ligands. We prepared a split-and-mix combinatorial library A that displays nucleophilic residues such as histidine and cysteine at the core position X and X and charged, hydrophobic, aromatic and polar residues in the other variable positions (Figure 1). Library A was tested for binding to aquocobalamin, and gave a few percent of darkly red-stained beads (Figure 1). Sequence determination revealed a consensus for cysteine residues at position X, together with an aspartate at X or X, and

Cobalamin (Cbl, vitamin B12) is an essential micronutrient that is synthesized only by bacteria. Mammals have developed a complex system for internalization of this vitamin from the diet. Three binding proteins (haptocorrin, intrinsic factor, transcobalamin (TC)) and several specific cell surface receptors are involved in the process of intestinal absorption, plasma transport and cellular uptake. The recent literature on the binding proteins is briefly reviewed. A structural study is presented addressing a unique feature of TC among the three proteins, i.e., the displacement of the weak Co(III)-ligand H2O at the upper (or beta) axial side of H2O-Cbl by a histidine side chain. We have investigated crystallographically the beta-ligand exchange on Cbl bound to TC by crystallization of bovine holo-TC in the presence of either cyanide or sulfite. The resulting electron density maps show that the histidine side chain has been displaced by an exogenous ligand CN(-) or SO(3)(-2)to a lower extent than expected based on their higher affinity for Co and excess concentration with respect to histidine. This may reflect either reduced affinities of CN(-) and SO(3)(-2)or the advantageous binding of the protein-integrated His-residue when competing for the beta-site of Cbl bound to TC. The loop hosting the histidine residue appears more flexible after disruption of the coordination bond His-Cbl but no other differences are observed in the overall structure of holo-TC. These structural results are discussed in relation to a possible physiological role of histidine substitution for H2O and regarding the role of beta-conjugated Cbl-analogues recently proposed for targeted delivery of imaging agents.

Fluorescent probe rhodamine was appended to 5' OH-ribose of cobalamin (Cbl). The prepared conjugate, CBC, bound to the transporting proteins, intrinsic factor (IF) and transcobalamin (TC), responsible for the uptake of Cbl in an organism. Pronounced increase in fluorescence upon CBC attachment facilitated detailed kinetic analysis of Cbl binding. We found that TC had the same affinity for CBC and Cbl (K(d) = 5 x 10(-15) m), whereas interaction of CBC with the highly specific protein IF was more complex. For instance, CBC behaved normally in the partial reactions CBC + IF(30) and CBC + IF(20) when binding to the isolated IF fragments (domains). The ligand could also assemble them into a stable complex IF(30)-CBC-IF(20) with higher fluorescent signal. However, dissociation of IF(30)-CBC-IF(20) and IF-CBC was accelerated by factors of 3 and 20, respectively, when compared to the corresponding Cbl complexes. We suggest that the correct domain-domain interactions are the most important factor during recognition and fixation of the ligands by IF. Dissociation of IF-CBC was biphasic, and existence of multiple protein-analogue complexes with normal and partially corrupted structure may explain this behaviour. The most stable component had K(d) = 1.5 x 10(-13) m, which guarantees the binding of CBC to IF under physiological conditions. The specific intestinal receptor cubilin bound both IF-CBC and IF-Cbl with equal affinity. In conclusion, the fluorescent analogue CBC can be used as a reporting agent in the kinetic studies, moreover, it seems to be applicable for imaging purposes in vivo.

Phenylketonuria (PKU) is caused by an autosomal recessive deficiency of the enzyme phelnylalanine hydroxylase leading to a failure to convert phenylalanine to tyrosine. To avoid irreversible neurological damage because of increased phenylalanine, treatment is instituted rapidly after birth. We examined 31 adult PKU patients living on a less protein-restricted diet. Theoretically, these PKU patients had an increased risk of developing vitamin B(12) and B(6) deficiency because of a limited intake of animal products. Besides laboratory tests (n = 31) we obtained clinical information (n = 30) and detailed information on food consumption (n = 28). Three-quarters of the patients had early biochemical signs of vitamin B(12) deficiency. In spite of a normal folate status, 9 (29%) had a plasma homocysteine above 12 micromol/L. In accord with these findings, the food questionnaires indicated that 11 (39%) patients received less than the recommended daily vitamin B(12), and 20 (71%) received less vitamin B(6) than recommended. A significant association was found between reduced vitamin B(12) intake and both reduced serum cobalamins (p = 0.04) and reduced serum transcobalamin saturation (p = 0.03). Eleven patients took a vitamin pill daily, and these patients had a significantly lower plasma homocysteine compared to the rest. The present study suggests that adult PKU patients were at increased risk of developing vitamin B(12) deficiency, and their intake of vitamin B(6) was below the recommended daily intake. In conclusion PKU patients need continuing dietary guidance throughout adult life, and considering the risks, costs and potential benefits, daily vitamin supplementation seems justified in these patients.

BACKGROUND: Autism is a behaviorally defined neurodevelopmental disorder usually diagnosed in early childhood that is characterized by impairment in reciprocal communication and speech, repetitive behaviors, and social withdrawal. Although both genetic and environmental factors are thought to be involved, none have been reproducibly identified. The metabolic phenotype of an individual reflects the influence of endogenous and exogenous factors on genotype. As such, it provides a window through which the interactive impact of genes and environment may be viewed and relevant susceptibility factors identified. OBJECTIVE: Although abnormal methionine metabolism has been associated with other neurologic disorders, these pathways and related polymorphisms have not been evaluated in autistic children. METHODS: Plasma levels of metabolites in methionine transmethylation and transsulfuration pathways were measured in 80 autistic and 73 control children. In addition, common polymorphic variants known to modulate these metabolic pathways were evaluated in 360 autistic children and 205 controls. RESULTS: The metabolic results indicated that plasma methionine and the ratio of Sadenosylmethionine (SAM) to S-adenosylhomocysteine (SAH), an indicator of methylation capacity, were significantly decreased in the autistic children relative to age-matched controls. In addition, plasma levels of cysteine, glutathione, and the ratio of reduced to oxidized glutathione, an indication of antioxidant capacity and redox homeostasis, were significantly decreased. Differences in allele frequency and/or significant gene-gene interactions were found for relevant genes encoding the reduced folate carrier (RFC 80G > A), transcobalamin II (TCN2 776G > C), catechol-O-methyltransferase (COMT 472G > A), methylenetetrahydrofolate reductase (MTHFR 677C > T and 1298A > C), and glutathione-Stransferase (GST M1). CONCLUSION: We propose that an increased vulnerability to oxidative stress (endogenous or environmental) may contribute to the development and clinical manifestations of autism.

Women who take folic acid in the periconceptional period greatly reduce their chances of having a child with a neural tube defect (NTD). Using multivitamins may also reduce the risk of having a child with an omphalocele. In this study, we tested single nucleotide polymorphisms in folate-related enzyme genes for association with omphalocele. Polymorphisms in methylenetetrahydrofolate reductase (MTHFR), methylenetetrahydrofolate dehydrogenase (MTHFD1), the reduced folate carrier (SLC19A1), and transcobalamin II (TCN2) were examined in 25 children with euploid omphalocele and 59 matched controls. Omphalocele cases were significantly more likely to carry the T allele of MTHFR 677C T, a known risk factor for NTDs (odds ratio 3.50, 95% confidence interval 1.07–11.47, P = 0.035). The MTHFD1 R653Q, SLC19A1 R27H, and TCN2 P259R polymorphisms showed no significant association with omphalocele. In this small study, the thermolabile variant of MTHFR, 677C T, was associated with an increased risk for omphalocele. This variant causes reduced enzyme activity, thus suggesting a mechanism by which multivitamins with folic acid might prevent omphalocele. Additional investigation is required. Published 2005 Wiley-Liss, Inc.

This review describes the early chronological events in the pursuit of a treatment for pernicious anaemia, and the subsequent discovery of vitamin B12 and the intrinsic factor. It details Castle's experiments which established the theory of extrinsic and intrinsic factors as hemopoietic principles, and describes the studies on purification of the anti-pernicious anaemia principle from liver tissue that terminated in the crystallization of vitamin B12 and identification of its coenzyme forms. Biochemical purification and characterization of the intrinsic factor secreted by the gastric parietal cells, and two other vitamin B12 proteins, R-binder (transcobalamin I, haptocorrin), and transcobalamin II, are discussed in detail. The biochemical reactions in micro-organisms and humans in which vitamin B12 is involved are then briefly reviewed, and finally and briefly the immunological basis of pernicious anaemia is discussed.

Uniformly (13)C,(15)N-labeled MutS, the coenzyme B(12)-binding subunit of glutamate mutase from Clostridium tetanomorphum, was prepared by overexpression from an Escherichia coli strain. Multidimensional heteronuclear NMR spectroscopic experiments with aqueous solutions of (13)C,(15)N-labeled MutS provided signal assignments for roughly 90% of the 1025 hydrogen, 651 carbon, and 173 nitrogen atoms and resulted in about 1800 experimental restraints. Based on the information from the NMR experiments, the structure of MutS was calculated, confirming the earlier, less detailed structure obtained with (15)N-labeled MutS. The refined analysis allowed a precise determination of the secondary and tertiary structure including several crucial side chain interactions. The structures of (the apoprotein) MutS in solution and of the B(12)-binding subunit in the crystal of the corresponding homologous holoenzyme from Clostridium cochlearium differ only in a section that forms the well-structured helix alpha1 in the crystal structure and that also comprises the cobalt-coordinating histidine residue. In the apoprotein MutS, this part of the B(12)-binding subunit is dynamic. The carboxy-terminal end of this section is conformationally flexible and has significant propensity for an alpha-helical structure ("nascent helix"). This dynamic section in MutS is a decisive element for the binding of the nucleotide moiety of coenzyme B(12) and appears to be stabilized as a helix (alpha1) upon trapping of the nucleotide of the B(12) cofactor.

Insolubilized antibody to transcobalamin I was used to separate transcobalamin I and transcobalamin II. By bioautography of the extracted cobalamins it was shown that transcobalamin II bound more deoxyadenosylcobalamin than did transcobalamin I, and that methylcobalamin accounts for most of the cobalamins attached to transcobalamin I. This finding may indicate that transcobalamin I has a function in the metabolism of methylcobalamin in man.

Objectives/Hypothesis In contrast to normal epithelium, the desquamating stratified squamous epithelium of temporal bone cholesteatoma characteristically exhibits sustained hyperproliferative growth and a capacity for bone erosion. We conducted genome-wide microarray analyses to determine the molecular nature of cholesteatoma's biological processes and identify disease-associated, altered gene activity. We tested the hypothesis that genes contributing to the pathophysiology of cholesteatoma are differentially expressed compared to control tissue. Study Design Prospective experimental analysis. Methods Using new, enhanced microarray platforms and well-annotated human transcriptome probes, we measured global gene expression levels in surgical specimens of cholesteatoma and in the corresponding normal postauricular skin in four patients. Genes of interest were verified by quantitative real time reverse transcriptase polymerase chain reaction analyses using cholesteatoma and postauricular sample pairs (n = 13). External auditory canal skin from six additional patients was also evaluated as a normal control. Immunohistochemistry detected protein expression in tissue sections and the cells involved. Results DNA chip analyses identified 282 differentially expressed genes in cholesteatoma compared to control samples. Of these, 104 genes were upregulated and 178 were downregulated. Ontological classifications indicate relationships to cellular processes including receptor binding, cell communication and motion, vitamin metabolism, and cytokine-mediated inflammation. Based on potential involvement in disease pathology, 10 genes were selected and independently verified by quantitative polymerase chain reaction. Immunohistochemical detection of transcobalamin-1 and CCL27 implicates cholesteatoma keratinocytes and dermal endothelial cells as contributors in disease processes. Conclusions We present a comprehensive, human genome-wide survey of disease-associated gene expression that extends the public database and provides new evidence for molecular mechanisms involved in cholesteatoma pathology. Laryngoscope, 123:S1–S21, 2013

OBJECTIVES: To determine the clinical significance of subnormal serum vitamin B12 concentration in older people by comparing the hematological, neurological, and biochemical findings in patients with subnormal serum B12 with a control group with normal B12 levels. DESIGN: Clinical and laboratory assessment of hospital patients selected to represent a wide range of serum B12 levels. SETTING: Patients in the medical wards of two hospitals, one a general hospital and the other a geriatric hospital. PARTICIPANTS: Ninety-four older patients, 43 with subnormal (

Plasma gastrin concentration increases in late gestation and reaches a peak at birth or shortly after birth in many species (‘neonatal hypergastrinaemia’). We investigated the hypothesis that gastrin and gastric acid secretion in the neonate is influenced by the final rise in plasma cortisol associated with spontaneous (vaginal) birth. Caesarean-delivered (CD, n = 28) or vaginally delivered (VD, n = 24) premature or full-term piglets (97–115 days gestation) were killed immediately after birth (using pentobarbitone). Compared with newborn CD pigs, the newborn VD pigs had significantly higher (P < 0.05) concentrations of cortisol (669 +/− 60 versus 223 +/− 2 nM) and gastrin (57 +/− 4 versus 33 +/− 1 pM) in plasma, and significantly lower gastric fluid pH (3.3 +/− 0.2 versus 4.7 +/− 0.3), amidated (bioactive) gastrin in the antrum (550 +/− 77 versus 1220 +/− 29 pmol g-1) and glycine-extended (precursor) gastrin in the antrum (81 +/− 10 versus 143 +/− 5 pmol g-1). There were significant linear correlations between log plasma cortisol values and plasma gastrin (r = 0.40, P < 0.05) or gastric fluid pH (r = -0.51, P < 0.05) in newborn pigs. The effects of cortisol in the immediate postnatal period were investigated in forty-one CD pigs born at 111-112 days gestation and treated with saline, metyrapone (an inhibitor of cortisol synthesis) or adrenocorticotrophic hormone (ACTH) from 0 to 7 days after birth. At 7 days, plasma gastrin in ACTH-treated pigs (elevated plasma cortisol) was significantly lower than in saline-treated pigs, but not different from that in metyrapone-treated pigs (low plasma cortisol). No treatment effects were observed postnatally for antral gastrin and fundic cobalamin-binding protein concentrations. These results suggest that in the intrapartum period the high circulating cortisol levels stimulate the normal rise in gastrin and acid secretion associated with spontaneous vaginal delivery in the piglet, whereas postnatally, cortisol is unlikely to play an important role in the subsequent development of gastrin and acid secretion.

A cohort of asymptomatic human immunodeficiency virus (HIV) seropositive patients was followed over a 2 1/2-year period, to establish changes in serum vitamin B12 (B12) concentrations. Serum B12, CD4 count, and clinical progression to acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) were measured. The unsaturated B12 binding capacities of the transcobalamins were also determined at the start of the study and compared to those from a homosexual HIV seronegative control group. The geometric mean of serum B12 in 218 asymptomatic HIV seropositive patients was significantly lower than of a homosexual HIV seronegative control group (P = 0.02) and the unsaturated B12 binding capacities of transcobalamins I and II were significantly higher in the asymptomatic patients compared with the same control group (P < 0.03, P < 0.0001, respectively). Fifty-nine of the asymptomatic HIV seropositive patients were followed over a 2 1/2-year period during which most had falling serum B12 levels (64%). Twelve patients progressed clinically to ARC or AIDS, of which nine had repeat serum B12 estimation prior to progression. All nine patients had or developed falling serum B12 levels without any evidence of an HIV-related bowel disorder. All patients progressing had falling CD4 counts. Subnormal serum B12 levels are common in HIV disease and occur at an early stage. B12 levels fall in most patients with time and may help predict those patients whose disease will progress the most rapidly. © 1994 Wiley-Liss, Inc.

Transcobalamin II deficiency is a rare, probably autosomal recessive, inborn error of protein metabolism [Hakami et al., 1971]. Several authors have described the morphological characteristics of bone marrow aspirates from patients with this disorder; no reports have detailed the cytogenetic findings [Hitzig et al., 1974; Hakami et al., 1971; Niebrugge et al., 1982]. We report the cytogenetic findings of the bone marrow aspirates from an infant with transcobalamin II deficiency and identify fragile site expression in the hematopoietic cells in this patient.

We have recently reported a new and rapid assay to measure plasma holotranscobalamin II (holo TC II) as a means of exploring vitamin B12 status. In order to further evaluate the significance of plasma holoTC II in determining tissue cobalamin, we have chosen the red blood cell-vitamin B12 (RBC-B12) assay as a measure of tissue vitamin B12 content and studied the relationship between RBC-B12 and plasma holoTC II levels. Plasma holoTC II and RBC-B12 concentrations were concomitantly assayed in 20 hematologically normal controls and cancer patients. In our groups of controls, the mean value of RBC-B12 was determined as 241 +/- 51 pg/ml of packed erythrocytes (PE) with a range varying from 180 to 355 pg/ml PE. Preliminary results obtained in 32 cancer patients revealed lower holoTC II and RBC-B12 levels than the control group and a required threshold value of 70 pg/ml of holoTC II in order to maintain a normal RBC-B12 greater than 180 pg/ml PE.

Cobalamin (Cbl, vitamin B12) metabolism was analyzed in cultures of human chorionic villus (CV) cells obtained at 9–10 weeks of gestation. CV cells were shown to synthesize transcobalamin II (TCII) and to possess a high affinity receptor for that molecule. The cells bound and internalized radioactive cyanocobalamin (CN[57Co]Cbl) complexed to TCII. This internalized CN[57Co]Cbl was found to be converted to both methylCbl and adenosylCbl, the two intracellular coenzyme forms of Cbl, and bound to the two known intracellular Cbl requiring enzymes, methionine synthase (MS) and methylmalonyl-CoA mutase. Both enzyme systems were found to be functional in the intact cell by demonstrating the incorporation of the radioactive label from both [14C]CH3-tetrahydrofolate and [14C]propionate into acid insoluble products. MS activity was also detected in lysed cell material. CV cells were shown not to be auxotrophic for methionine since they were able to utilize homocysteine in place of methionine for cell division. Since CV cells are capable of performing many of the complex events associated with Cbl metabolism, it may be possible to use these cells to diagnose genetic defects of Cbl metabolism. © 1993 Wiley-Liss, Inc.

A 24-year old black man with hemoglobin SC was hospitalized in 2003 because of a 5-day history of fever, headache, and diffuse joint pains; a longer history of tiredness; and an unexplained 30-lb weight loss in the past year. He had been minimally symptomatic all his life, other than one presumed crisis with pneumonia at the age of 12 years. In 2002 and 2003, however, he required hospitalization and antibiotics elsewhere twice for presumed crises with pneumonia. He was taking no medications other than daily folic acid and denied drug or alcohol abuse.

Thirty-four symptomatic cases of inherited transcobalamin II (TCII) deficiency were analysed in order to determine the frequency and nature of neurologic manifestations. In no instance was there definite evidence of a neurologic disorder at the time of presentation as a young infant. One child of 2 1/2 years transiently lost deep tendon reflexes at a time of suboptimal treatment. A syndrome of mental retardation and other neurologic manifestations was observed in three cases, all with the following in common: (1) an extended duration of illness of 2-17 years; (2) inadequate or not treatment with Cbl; (3) treatment with folic of folinic acid. TCII deficiency rarely if ever presents with neurologic manifestations. However, neurologic disorders can be produced subsequently by improper treatment.

In AIDS, as previously found in pernicious anemia (PA), the earliest serum marker of subnormal vitamin B12 (cobalamin) absorption, and therefore of negative B12 balance, is low serum holotranscobalamin II (holo-TC II; B12-TC II) despite normal total serum B12 level, normal serum homocysteine, and normal classic (oral free radio-B12) Schilling test. This may be accompanied by subtle and insidious damage to hematopoietic, immunologic, neuropsychiatric, nutritional and alimentary systems, confirmed by correction on therapeutic trial with B12 therapy. Our studies suggest such selective B12 deficiency occurs in about half of the HIV-1 infected, in part due to frequent depression of B12 absorption by HIV-1 attack on the gastric mucosa and/or opportunistic infection attack on the small bowel, and in part due to a telescoping of the continuum of the stages of negative B12 balance in relation to damage to B12 delivery by the infective and/or systemic disease process. In AIDS, when total serum B12 is normal despite tissue depletion of B12, if the classic Schilling test does not reveal subnormal food B12 absorption, the food Schilling test does. We hypothesize that DNA-synthesizing cells of the hematopoietic, immunologic, neurologic and other systems which have surface receptors solely for holo-TC II, and which have low B12 stores, rapidly become dysfunctional due to B12 deficiency when holo-TC II is low, while cells (such as liver cells) which also have surface receptors for holohaptocorrin (B12-haptocorrin) remain B12-replete. We believe this to be another example of the concept of selective nutrient deficiency in one cell line but not another.

A cDNA encoding the gastric haptocorrin was isolated from a porcine gastric mucosal lambda gt11 cDNA library using oligonucleotide probes. The 1.4-kb cDNA contains a 1.25-kb open reading frame and 178 nucleotides of 3' noncoding region. Although no initiator methionine is present, primer extension analysis indicated that the transcription initiation site is only 100 bp upstream of the 5' end of this clone. Northern blot analysis showed that a single mRNA species of 1.6 kb exists in hog gastric mucosa. There was no cross-hybridization between this cDNA and the mRNA for haptocorrin in rat submaxillary gland or gastric RNA by Northern blot analysis. This lack of cross-reactivity was also seen on Southern blots, where cow, sheep and dog but neither rat nor mouse genomic DNAs showed cross-hybridizing bands. Comparison of the deduced amino acid sequence of this cDNA with that previously reported for rat intrinsic factor [Dieckgraefe, B.K. et al. (1988) Proc. Natl Acad. Sci. USA 85, 46-50] showed considerable similarity, suggesting that these cobalamin-binding proteins may have a common evolutionary origin.

This study introduces a simple, reproducible assay for HLA class I antigen using antibodies against beta 2-microglobulin and the heavy chain on HLA. The sandwich technique was named mixed enzyme-linked immunosorbent assay (MELISA), and was designed for identification of plasma membranes in neutrophil subcellular fractions. The subcellular localization of HLA was identical to that of other plasma membrane markers, [3H]concanavalin A and detergent-independent alkaline phosphatase, and was unchanged by stimulation of cells by weak and strong secretagogues. In addition to the presence as part of the HLA complex in the plasma membrane uncomplexed beta 2-microglobulin is present in the specific granules of neutrophils. However, the release of beta 2-microglobulin from intact neutrophils stimulated with formyl-methionylleucylphenylalanine was much higher than could be explained by exocytosis of specific granules. Subcellular fractionation studies demonstrated that beta 2-microglobulin is localized in fractions characterized by latent alkaline phosphatase and released from this novel secretory compartment in response to stimulation with formyl-methionylleucylphenylalanine.

When dialysed rat serum which contains a single, low molecular weight binder for vitamin B12, rat transcobalamin II (rat TC-II), was labelled in vitro with 57Co-vitamin B12 and then incubated at 30 degrees C (pH 7-5) with vesicles of highly purified plasma membranes separated from microsomal fractions of rat liver by density gradient centrifugation, the 57Co-vitamin B12-rat TC-II complex bound to high affinity sites on the vesicles via a specific (binding after correction for 'non-specific' binding in the presence of a large excess of the non-radioactive complex), saturable, and reversible interaction. The apparent affinity constant for the binding reaction was 5-5 X 10(9) M-1. Using the same incubation conditions, free vitamin B12 also bound to the vesicles of plasma membranes via a specific, saturable, but apparently irreversible interaction. Preincubation of the membranes with free vitamin B12 did not interfere with the subsequent binding of the vitamin B12-rat TC-II complex to the membranes; however, preincubation with the vitamin B12-rat TC-II complex did interfere, to some extent, with the subsequent binding of free vitamin B12. Dialysed rat serum, perhaps the free rat TC-II in the dialysed serum, also inhibited the binding of the vitamin B12-rat TC-II complex to the plasma membranes. The relationship of the binding sites identified in this report to the absorption of vitamin B12 by rat liver, and thus their physiological significance remains unknown until further work is done, perhaps using intact hepatocytes.

Transcobalamin (TC) II, the cellular membrane carrier of vitamin B 12 has recently attracted attention as an acute phase reactant in autoimmune disorders and reticuloendothelial malignancies. In a prospective clinical evaluation, 20 patients presenting with proven metastatic renal adenocarcinoma underwent nephrectomy and were followed till death, or at least 3 years. Two patients obtained a complete remission. TCII was significantly elevated (P less than 0.005) preoperatively and varied with activity of the carcinoma, supplementing the erythrocyte sedimentation rate and fibrinogen. The postoperative response and pattern of TCII activity correlated with disease progression. No relation was found to liver metastases. This study supports the recent findings of TCII as an indicator of activity in disorders affecting the immune mechanisms probably acting as an acute phase reactant, and is a useful supplement in renal adenocarcinoma.

We undertook a study to define the role of cyclic AMP [cAMP] in modulating the secretion of transcobalamin II (TC-II) in the mouse macrophage like cell line J774. J774 was observed to secrete large amounts of TC-II, particularly in the presence of 8-bromo cAMP or cholera toxin or when grown in medium supplemented with low concentrations of horse serum (1% or 5%) or in serum-free medium. Variant cell lines derived from J774 and deficient either in adenylate cyclase (ac -) or cAMP-dependent protein kinase (pk -) activity showed very low and intermediate levels of basal secretory activity of TC-II, respectively, compared to J774. Maximum secretory activity of TC-II was observed in J774 under conditions in which growth was poorest (in the presence of 8-bromo-cAMP or 1% or 5% horse serum-supplemented medium or in serum-free medium). Cells grown in serum-free medium were found to have elevated basal adenylate cyclase activity and cAMP levels compared to those grown in medium supplemented with 20% horse serum. The data from this study demonstrate a negative correlation between growth activity and TC-II secretion in the J774 cell line. The stimulatory effect of exogenous cAMP on TC-II secretion by J774, the reduced secretory activity of the variant lines ac- and pk- and the observed increase in cell cAMP levels under conditions of serum starvation in which TC-II secretion is considerably enhanced, suggest that cell cAMP is an important modulator of TC-II secretion and growth behavior in the J774 cell line.

Granulocytes from a 6-year-old boy with congenital transcobalamin II (TC II) deficiency were found to have abnormally low antibacterial activity against Staphylococcus aureus and very low intracellular levels of the cobalamin coenzymes. Transfusion of hydroxocobalamin (OH-Cbl) bound to normal plasma temporarily restored granulocyte bactericidal activity and increased cellular levels of the cobalamin coenzymes. Granulocyte function was also temporarily restored by oral Leucovorin. The defect appeared to be causally related to the patient's TC II deficiency and indirectly to a deficiency of cobalamin and folate coenzymes.

A 39-year-old woman presented with mild anemia, glossitis, an increased MCV, a low serum cobalamin (Cbl) (vitamin B12), mild tissue deficiency of Cbl, but with neither malabsorption of Cbl, impaired intake, nor deficiency of or inactivity of transcobalamin II (TC II). Because of a persistently low holo-TC II (TC II carrying Cbl as the circulating complex of TC II-Cbl), much of the evaluation was focused on the patient's TC II. Her TC II promoted the uptake of Cbl, reacted with anti-TC II, and bound Cbl in vitro. A test dose of 200 micrograms of cyanocobalamin (CN-Cbl) i.m. increased her holo TC II to levels higher than those in healthy persons, but with a much more abrupt fall to a subnormal level. Two milligrams of CN-Cbl i.m. followed by 100 micrograms i.m. monthly failed to maintain normal amounts of circulating TC II-Cbl or to overcome the tissue deficiency of Cbl. One milligram i.m. weekly or daily p.o. corrected both. The low holo TC II was considered to be responsible for the clinical expression and may have been primary to the reduced amounts of total and holo R binder of Cbl in the circulation. This study of a newly recognized defect points out the need for circulating holo TC II, a rational use of pharmacologic amounts of Cbl, and a possible interrelationship between TC II and the R binder of Cbl.

Summary. Intrinsic factor (IF) and cobalamin-R-binding protein (R-binder) linked to polyacrylamide beads were used to absorb cobalamins from solutions and serum extracts. Both binding agents were equally effective in removing [57Co]B12 from aqueous solution. IF was more effective than R-binder in removing [57Co]B12 added to a serum extract. All endogenous cobalamins detectable in serum by saturation analysis assay were removed by absorption onto R-binder. Absorption with IF removed microbiologically-active cobalamins but left behind analogues assay able, with an R-binder. However, when absorption with IF was continued the concentration of R-binding cobalamins steadily declined indicating that IF bound both types of cobalamins though the binding was less avid for the microbiologically-inactive analogues than for microbiologically-active cobalamins. Finally, the R-binding analogues in serum were carried on transcobalamin I and none was detectable on transcobalamin II. The absorption studies establish the presence of two types of cobalamins one binding preferentially to IF and the other preferentially to R-binder. Only the former is detected by microbiological assay.