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Rare sugars are monosaccharides with low natural abundance. They are structural isomers of dietary sugars, but hardly be metabolized. Here, we report that rare sugar L-sorbose induces apoptosis in various cancer cells. As a C-3 epimer of D-fructose, L-sorbose is internalized via the transporter GLUT5 and phosphorylated by ketohexokinase (KHK) to produce L-sorbose-1-phosphate (S-1-P). Cellular S-1-P inactivates the glycolytic enzyme hexokinase resulting in attenuated glycolysis. Consequently, mitochondrial function is impaired and reactive oxygen species are produced. Moreover, L-sorbose downregulates the transcription of KHK-A, a splicing variant of KHK. Since KHK-A is a positive inducer of antioxidation genes, the antioxidant defense mechanism in cancer cells can be attenuated by L-sorbose-treatment. Thus, L-sorbose performs multiple anticancer activities to induce cell apoptosis. In mouse xenograft models, L-sorbose enhances the effect of tumor chemotherapy in combination with other anticancer drugs. These results demonstrate L-sorbose as an attractive therapeutic reagent for cancer treatment., (© 2023. The Author(s).)

The co-culture system of the fermentation process of vitamin C can be regarded as an artificial microbial ecosystem (AME). To extend our understanding of this AME, an investigation of the relationship between strains, substrate and product was carried out in this study. The results showed that both Ketogulonicigenium vulgare and 2-keto-L-gulonic acid (2-KLG, the precursor of vitamin C) can inhibit the growth of the helper strain, while the helper strain promoted the growth of K. vulgare and 2-KLG production. Moreover, L-sorbose is not only a substrate for 2-KLG production in the AME, but also a promoter of K. vulgare and an inhibitor of the helper strain. In the earlier stage of fermentation, the inhibition of L-sorbose on the helper strain's growth is a key factor for ensuring an efficient fermentation. In the condition of adding the extra helper strain (OD: 0.57, ratio of inoculation: 2%), the yields of 2-KLG is increased by 9% in the 14% L-sorbose medium. To the best of our knowledge, this is the first report about the inhibition of substrate in the AME of 2-KLG production.

In an attempt to develop D-sorbose as a new sweetener that could help in preventing lifestyle-related diseases, we investigated the inhibitory effect of D-sorbose on disaccharidase activity, using the brush border membrane vesicles of rat small intestines. The inhibitory effect was compared with that of L-sorbose and other rare sugars, and the small intestinal disaccharidases in rats was compared with that of humans as well. In humans and the small intestines of rats, d-sorbose strongly inhibited sucrase activity and weakly inhibited maltase activity. Inhibition by D-sorbose of sucrase activity was similar to that of L-arabinose, and the K(i) of D-sorbose was 7.5 mM. Inhibition by D-sorbose was very strong in comparison with that of L-sorbose (K(i), 60.8 mM), whereas inhibition of d-tagatose was between that of D-sorbose and L-sorbose. The inhibitory mode of D-sorbose for sucrose and maltase was uncompetitive, and that of L-sorbose was competitive. To determine a suppressive effect on postprandial blood levels of glucose and insulin via inhibition of sucrase activity, sucrose solution with or without D-sorbose was administered to rats. Increments in the blood levels of glucose and insulin were suppressed significantly after administration of sucrose solution with D-sorbose to rats, in comparison to administration of sucrose solution without D-sorbose. In contrast, the suppressive effect of L-sorbose on postprandial blood levels of glucose and insulin was very weak. These results suggest that D-sorbose may have an inhibitory effect on disaccharidase activity and could be used as a sweetener to suppress the postprandial elevation of blood levels of glucose and insulin. The use of D-sorbose as a sweetener may contribute to the prevention of lifestyle-related diseases, such as type 2 diabetes mellitus., (Copyright © 2014 Elsevier Inc. All rights reserved.)

D-Sorbose is naturally occurring rare sugar. In this study, we examined the effects of dietary D-sorbose in rats. Four-week-old male Sprague-Dawley rats were fed either an AIN-93G-based control diet or a 3% D-sorbose diet for 28 d. Body weight and body fat accumulation were not different between the two diet groups. Dietary supplementation of D-sorbose lowered the serum insulin level (*p<0.05) significantly compared to the control, although the glucose was not changed. In addition, the relative weight of the cecum increased significantly in the D-sorbose group (**p<0.01). These findings suggest that intake of D-sorbose may improve the glucose metabolism by reducing insulin secretion, and D-sorbose can be used as a food ingredient.

The genome of the ascomycete Neurospora crassa encodes CAO-1 and CAO-2, two members of the carotenoid cleavage oxygenase family that target double bonds in different substrates. Previous studies demonstrated the role of CAO-2 in cleaving the C40 carotene torulene, a key step in the synthesis of the C35 apocarotenoid pigment neurosporaxanthin. In this work, we investigated the activity of CAO-1, assuming that it may provide retinal, the chromophore of the NOP-1 rhodopsin, by cleaving β-carotene. For this purpose, we tested CAO-1 activity with carotenoid substrates that were, however, not converted. In contrast and consistent with its sequence similarity to family members that act on stilbenes, CAO-1 cleaved the interphenyl Cα-Cβ double bond of resveratrol and its derivative piceatannol. CAO-1 did not convert five other similar stilbenes, indicating a requirement for a minimal number of unmodified hydroxyl groups in the stilbene background. Confirming its biological function in converting stilbenes, adding resveratrol led to a pronounced increase in cao-1 mRNA levels, while light, a key regulator of carotenoid metabolism, did not alter them. Targeted Δcao-1 mutants were not impaired by the presence of resveratrol, a phytoalexin active against different fungi, which did not significantly affect the growth and development of wild-type Neurospora. However, under partial sorbose toxicity, the Δcao-1 colonies exhibited faster radial growth than control strains in the presence of resveratrol, suggesting a moderate toxic effect of resveratrol cleavage products.

We investigated responses of rice plant to three rare sugars, d-altrose, d-sorbose, and d-allose, due to establishment of mass production methods for these rare sugars. Root growth and shoot growth were significantly inhibited by d-allose but not by the other rare sugars. A large-scale gene expression analysis using a rice microarray revealed that d-allose treatment causes a high upregulation of many defense-related, pathogenesis-related (PR) protein genes in rice. The PR protein genes were not upregulated by other rare sugars. Furthermore, d-allose treatment of rice plants conferred limited resistance of the rice against the pathogen Xanthomonas oryzae pv. oryzae but the other tested sugars did not. These results indicate that d-allose has a growth inhibitory effect but might prove to be a candidate elicitor for reducing disease development in rice.

No anthelmintic sugars have yet been identified. Eight ketohexose stereoisomers (D- and L-forms of psicose, fructose, tagatose and sorbose), along with D-galactose and D-glucose, were examined for potency against L1 stage Caenorhabditis elegans fed Escherichia coli. Of the sugars, D-psicose specifically inhibited the motility, growth and reproductive maturity of the L1 stage. D-Psicose probably interferes with the nematode nutrition. The present results suggest that D-psicose, one of the rare sugars, is a potential anthelmintic.

D-Glucose uptake in germinating wild-type Aspergillus nidulans conidia is an energy-requiring process mediated by at least two transport systems of differing affinities for glucose: a low-affinity system (K(m) approximately 1.4 mM) and a high-affinity system (K(m) approximately 16 micro M). The low-affinity system is inducible by glucose; the high-affinity system is subject to glucose repression effected by the carbon catabolite repressor CreA and is absent in sorA3 mutant conidia, which exhibit resistance to L-sorbose toxicity. An intermediate-affinity system (K(m) approximately 400 micro M) is present in sorA3 conidia germinating in derepressing conditions. creA derepressed mutants show enhanced sensitivity to L-sorbose. The high-affinity uptake system appears to be responsible for the uptake of this toxic sugar.

The glucose transporter 5 (GLUT5)-a specific D-fructose transporter-belongs to a family of facilitating sugar transporters recently enlarged by the human genome sequencing. Prompted by the need to develop specific photolabels of these isoforms, we have studied the interaction of conformationally locked D-fructose and L-sorbose derived 1,3-oxazolidin-2-thiones and 1,3-oxazolidin-2-ones to provide a rational basis for an interaction model. The inhibition properties of the D-fructose transporter GLUT5 by glyco-1,3-oxazolidin-2-thiones and glyco-1,3-oxazolidin-2-ones is now reported. In vitro, the fused-rings systems tested showed an efficient inhibition of GLUT5, thus bringing new insights on the interaction of D-fructose with GLUT5.

L-Sorbose has previously been assumed to stimulate cellulase formation in an indirect manner, different from that of sophorose in Trichoderma reesei. Through Northern blot analysis however, L-sorbose was found to regulate coordinately six cellulase genes (including eg13, whose behavior has not been studied so far) at transcriptional level, as is the case with sophorose in T. reesei strains PC-3-7 and QM9414. Dot blot analysis showed that the proportions of each cellulase mRNA to cbh1 mRNA, the largest amount of mRNA transcribed in T. reesei, did not change when L-sorbose or sophorose was used as an inducer in the PC-3-7 and QM9414 strains. cbh2 and egl1 mRNAs were about 45-60% and 20-30% of the cbh1 transcript, whereas small amounts of mRNA, 1-2% of cbh1, were observed on other endoglucanase genes. Furthermore, the PC-3-7 strain showed an enhanced level of cellulase gene transcription, about two- and four- to six-fold higher than that of the QM9414 strain with sophorose and L-sorbose, respectively.

Human Cu,Zn-superoxide dismutase (SOD) was incubated with various intermediates of the Maillard reaction and glycolytic pathway (arabinose, glyoxal, glycolaldehyde, glyceraldehyde, glyceraldehyde 3-phosphate, and dihydroxyacetone) and some reducing sugars (sorbose, xylose, and ribose). The change of the activity and the molecular weight were measured and compared with that of SOD incubated with glucose or fructose. Sorbose, xylose, and ribose decreased the activity with a rate comparable to fructose. Site-specific and random fragmentation were observed upon the incubation with them. Arabinose showed a similar inactivation rate as glucose. The intermediates other than arabinose had a high inactivation rate. Especially, glyceraldehyde, glycolaldehyde, and glyoxal most strongly lowered the activity in a concentration-dependent manner and a significant inactivation was recognized even at 1 mM level. SDS-PAGE band patterns indicated that the inactivation by those carbonyl compounds occurred by both crosslinking and site-specific fragmentation of SOD.

We have cloned a 3.4 kb DNA fragment from the chromosome of Klebsiella pneumoniae that codes for a phosphoenolpyruvate-dependent L-sorbose: phosphotransferase system (PTS). The cloned fragment was sequenced and four open reading frames coding for 135 (sorF), 164 (sorB), 266 (sorA) and 274 (sorM) amino acids, respectively, were found. The corresponding proteins could be detected in a T7 overexpression system, which yielded molecular masses of about 14,000 for SorF, 19,000 for SorB, 25,000 for SorA and 27,000 for SorM. SorF and SorB have all the characteristics of soluble and intracellular proteins in accordance with their functions as EIIASor and EIIBSor domains of the L-sorbose PTS. SorA and SorM, by contrast, are strongly hydrophobic, membrane-bound proteins with two to five putative transmembrane helices that alternate with a series of hydrophilic loops. They correspond to domains EIICSor and EIIDSor. The four proteins of the L-sorbose PTS resemble closely (27%-60%) the four subunits of a D-fructose PTS (EIIALev, EIIBLev, EIICLev, and EIIDLev) from Bacillus subtilis and the three subunits of the D-mannose PTS (EIIA,BMan, EIICMan, and EIIDMan) from Escherichia coli K-12. The three systems constitute a new PTS family, and sequence comparisons revealed highly conserved structures for the membrane-bound proteins. A consensus sequence for the membrane proteins was used to postulate a model for their integration into the membrane.

The effect of dietary sorbose on diabetes after the incidence of the syndrome in the nonobese diabetic mouse was investigated in the animals from 8 to 14 weeks of age. When sucrose (200 g/kg diet) in a control diet was replaced by sorbose, the body weight and the blood glucose concentration were significantly reduced, but the serum insulin concentration was unchanged. The urinary glucose concentration was the same for both sucrose and sorbose diets. It is suggested that after the incidence of diabetes, dietary sorbose could not improve urinary excretion of glucose, even though sorbose could reduce the blood glucose concentration.

The cause of species difference in the susceptibility of erythrocytes to L-sorbose, and the difference in the hemolytic effect of sorbose on high potassium-containing (HK) and low potassium-containing (LK) canine erythrocytes were examined. L-Sorbose was phosphorylated in canine erythrocytes, but not in human erythrocytes. Furthermore, sorbose-1-phosphate, a metabolite of L-sorbose, strongly inhibited the hexokinase of LK canine erythrocytes, but not that of HK canine erythrocytes. These results strongly indicated that inhibition of hexokinase by sorbose-1-phosphate in LK erythrocytes induced severe glycolytic limitation in these cells, resulting in hemolysis, and that HK erythrocytes are resistant to sorbose-induced hemolysis because these cells have a high hexokinase activity.

Experiments were conducted to determine the effect of sorbose on feed consumption, egg production and size, and cholesterol metabolism of laying hens. In Experiment 1, 87-wk-old laying hens (10 per treatment) were fed diets containing 0, 10, or 20% sorbose for 4 wk. In a second experiment, 108-wk-old laying hens (eight per treatment) were fed a control diet, a diet with 10% added sorbose, or the control diet with intake restricted to the level of sorbose-treated hens for 4 wk. Feed consumption and egg production were recorded daily. Plasma and egg cholesterol levels were determined at 0, 2, and 4 wk. Plasma and egg very low density lipoprotein (VLDL) concentrations were determined after 4 wk. Egg production, feed intake, and body weight gain were significantly reduced by dietary sorbose. Egg and yolk weight and percentage yolk decreased in response to sorbose. Sorbose significantly reduced plasma cholesterol and VLDL by approximately 50%, compared with the hens fed a control diet. Egg cholesterol concentration (milligrams per gram of yolk) was significantly increased, although the reduction in yolk size resulted in similar total egg cholesterol (milligrams per egg). Restricting feed intake of laying hens significantly lowered plasma cholesterol, but not to levels comparable to that of sorbose-treated hens. The data indicate that substantial reduction of plasma cholesterol and VLDL by dietary sorbose was not accompanied by reduced egg cholesterol.

The effect of dietary sorbose on the prevention (Experiment 1) and amelioration (Experiment 2) of diabetes was investigated in the genetically diabetic mouse [C57BL/KsJ (db/db)] for 6 wk. When sucrose (200 g/kg diet) in a control diet was replaced by sorbose, the blood glucose concentration was dramatically lower, but the serum insulin concentrations did not differ. When mice were fed the diets before the onset of diabetic symptoms, glucose excretion in urine was prevented in the mice fed the sorbose diet, but mice fed the control diet excreted glucose in the urine, and the concentration increased with age. When dietary treatment began after the development of diabetic symptoms, dietary sorbose greatly reduced the incidence of hyperglycemia and lowered urinary glucose excretion, compared with mice fed the sucrose-containing diet. These results suggest that dietary sorbose might be useful in patients with, or at risk of developing, noninsulin-dependent diabetes, both before and after exhibiting the syndrome.

1. The hemolytic effect of L-sorbose on canine erythrocytes characterized by inherited high Na, K-ATPase activity and a high potassium concentration (HK RBCs) was compared with that on normal canine erythrocytes (LK RBCs). 2. Dogs having HK RBCs (HK dogs) revealed no clinical and hematological changes after administration of L-sorbose, whereas normal dogs (LK dogs) developed severe hemolytic anemia associated with hemoglobinuria and marked decreases of erythrocyte ATP concentrations. 3. In vitro, L-sorbose induced hemolysis in LK RBCs along with the depression of both ATP and lactate formation in these cells, but not in HK RBCs. The inhibition of glycolysis by L-sorbose in LK RBCs, however, was not observed when glucose-6-phosphate was used as a substrate instead of glucose. 4. These results suggest that the disparity of susceptibility to sorbose-induced hemolysis may be due to the difference in erythrocyte metabolism between HK and LK RBCs, especially the high activity of hexokinase in HK cells, which was 2-fold greater than that in LK RBCs.

1. The influence of dietary sorbose on food intake and fatty acid synthesis of the liver and epididymal white adipose tissue (EWAT) was investigated in gold thioglucose (GTG)-injected obese mice from 12 to 14 weeks of age. 2. Sorbose was supplemented to a semi-purified diet at a level of 200 g/kg diet at the expense of sucrose. 3. On the last day of the experiment, fatty acids synthesis in the liver and EWAT was measured using an i.p. injection [1-14C]sodium acetate. 4. The decreases in body weight and food intake by dietary sorbose in GTG-injected obese mice were greater than those in control mice. 5. Lipid content and fatty acid synthesis in the liver and EWAT of control mice were not influenced by dietary sorbose. 6. In GTG-injected obese mice, the reduction of food intake by dietary sorbose suppressed fatty acid synthesis and lipid deposition in both liver and EWAT.

Glucan synthase activity of Neurospora crassa was isolated by treatment of protoplast lysates with 0.1% 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate and 0.5% octylglucoside in 25 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer, pH 7.4, containing 5 mM EDTA, 1 mM phenylmethylsulfonylfluoride, 200 mM inorganic phosphate, 10 microM GTP, 1 mM DTT, 10 mM sodium fluoride, and 600 mM glycerol. Resulting activity was partially purified by sucrose gradient density sedimentation. Approximately 70% of enzyme activity in the sucrose gradient peak fraction was soluble and enzyme activity was purified 7.3-fold. Partially purified enzyme activity had a half-life of several weeks at 4 degrees C, and a Km(app) of 1.66 +/- 0.28 mM. Inhibitors (Cilofungin, papulacandin B, aculeacin A, echinocandin B, sorbose and UDP) of 1,3-beta-D-glucan synthase activity were tested against crude particulate and detergent treated enzyme fractions and the Ki(app) of each inhibitor determined. It seems likely that this stable preparation of glucan synthase activity may be useful for in vitro enzyme screens for new glucan synthase inhibitors.

Male and female broilers were given diets (6 males and 6 females per diet) containing varying percentages of sorbose (0, 3, 6, and 9%) and fed for ad libitum access from 28 to 56 days of age. Body weight gain and feed intake were decreased with increasing dietary sorbose, particularly in male birds fed diets containing 9% sorbose, although feed efficiency and N retention rate were not influenced by dietary treatments. Absolute and relative abdominal fat weights were higher in females than in males and decreased with the increasing levels of dietary sorbose in both sexes. Fat content in the pectoral muscle also decreased as dietary sorbose increased. Dietary sorbose did not have significant effects on serum glucose, triglyceride, total cholesterol, low density lipoprotein, very low density lipoprotein, and chylomicron levels in either male or female birds. The ME values of diets decreased as dietary sorbose increased. Palmitic acid content of abdominal fat was significantly lower in birds fed the 9% sorbose diet than in birds fed the control diet. The reverse was true for linoleic acid content. It was concluded that dietary sorbose can be used as a potential regulator of lipid deposition in broilers.

Single Comb White Leghorn laying hens received ad libitum diets (10 birds per diet) containing varying concentrations of sorbose (0, 100, and 200 g/kg diet) for 4 wk. Body weight gain and feed intake decreased with increasing dietary sorbose. Serum triglyceride, cholesterol, low density lipoprotein, very low density lipoprotein, and chylomicron levels were significantly reduced, in dose-dependent fashions, as dietary sorbose increased, whereas serum glucose level remained unchanged by the dietary regimens. Absolute and relative weights of abdominal fat were also decreased by increasing dietary sorbose. Liver color improved; it became less white and less yellow with the supplement of dietary sorbose. Hen-day egg production rate was not affected with dietary sorbose, and hence, it has been shown that dietary sorbose can be used as a potential regulator of lipid metabolism in the laying hen.

Glucose administration inhibits the induction of ornithine aminotransferase (OAT) in both the whole animal and cultured hepatocytes. We have examined the ability of several hexoses and related molecules to inhibit the cAMP-dependent induction of OAT in primary cultures of adult rat hepatocytes. The hexoses (D-glucose, fructose, sorbitol, sorbose, and mannose) that were effective as inhibitors of OAT induction also resulted in accumulation of lactate in the culture medium, although lactate itself was not effective as an inhibitor. The hexoses and related 6-carbon structures (galactose, L-glucose, 2-deoxyglucose, 3-O-methylglucose, rhamnose, mannitol, and inositol) that were not effective as inhibitors of OAT induction did not result in accumulation of lactate in the culture medium. These results suggest that the carbohydrate repression of hepatic OAT requires metabolism of the carbohydrate by the liver cell. Upon addition to the culture medium of several compounds related to carbohydrate metabolism, many (ribose, xylitol, dihydroxyacetone, and glycerol) exhibited an inhibitory effect, with glycerol exhibiting the greatest effect. Fructose and glycerol inhibit OAT induction in the presence of 2-deoxyglucose, suggesting that the inhibitory effect of nonglucose carbohydrates is not occurring through conversion to glucose. The carbon sources observed to be most effective as inhibitors of OAT induction (glycerol, fructose, sorbitol, and sorbose result in more than 90% inhibition at 25 mM) all enter the glycolytic pathway at the triosephosphate level. The mechanism of the inhibitory effect of simple carbohydrates on OAT induction is not known but may involve an increase in certain glycolytic intermediates. Glucose and the related carbon sources exert their effect by inhibiting the cAMP-dependent increase in OAT synthesis. The cAMP-dependent increase in OAT mRNA was inhibited by fructose. These findings suggest that the carbohydrate inhibition of the cAMP-dependent increase in OAT synthesis occurs at a pretranslational level.

Oxygen uptake and glycolytic activity were studied in hepatocytes isolated from fed rats. The addition of fructose or tagatose resulted in a 38% and 31% inhibition of cellular respiration respectively. The addition of 10 mM D-glyceraldehyde caused a slight Crabtree effect. Glucose, L-sorbose, or glycerol failed to modify oxygen consumption. Only incubation in the presence of fructose showed a high aerobic glycolysis measured by lactate production.

Among the majority of Salmonella strains splitting sorbose or dulcitol with delay dimethylsulfoxide shortens the latent period preceding acid formation and abolishes the deceleration of sorbose adaption caused by salicine. In other strains, especially S. paratyphi B cultures, DMSO doesn't touch sorbose adaption directly but amplifies the restraing effect of salicine. From the whole of our findings it can be concluded that in the first group of strains sorbose adaption starts with segregation of adaptive sorbose permease positive mutants, followed by the - salicin-sensitive - induction of this permease, the appearance of mutants aditionally metabolizing sorbose constitutively, and, finally, the substrate-promoted particular growth of adapted cells. The latter category of strains, however, apparently possesses a wild type (constitutive or adaptive?) sorbose permease but splits off mutants with adaptive metabolizing enzymes the induction of which is salicine-sensitive. The amplification of the salicine effect by DMSO found in these strains might be refered to an enhancement of salicine uptake caused by DMSO.

Fermentation of sorbose by Salmonellae splitting this sugar with delay is restrained to a varying degree in presence of salicine, depending on the concentration of this glycoside. There is no support that salicine might become metabolized in this process. A similar salicine effect on the delayed fermentation of dulcitol has not been seen.

After growth on sucrose or glucose, Endomyces magnusii possess a monosaccharide uptake which resembles that of Saccharomyces cerevisiae (a high KT of uptake, preference for alpha-anomers of D-xylose and D-glucose, enhanced uptake during anaerobiosis, attainment of a diffusion equilibrium). The uptake is inhibited by other monosaccharides and especially strongly by D-galactose. In the absence of high concentrations of metabolizable sugars. E. magnusii develops a capacity to accumulate 3-O-methyl-D-glucose and D-xylose against a concentration gradient the new system displaying a high affinity for glucose (KT less than 0.1 mM), repression by glucose, mannose or galactose. Cycloheximide (0.2%) blocks the formation of the active system.

We have previously shown that monosaccharides and disaccharides will block the expression of spontneous monocyte-mediated cytotoxicity. Our data were consistent with the hypothesis that human mononuclear cells express lectin-like receptors that are capable of binding to a variety sugar moieties found on target cell membranes. In this communication, we will present evidence that monosaccharides and disaccharides are also capable of blocking the expression of T cell reactivity as measured by an in vitro antigen-specific proliferative assay. The majority of sugars that blocked monocyte-mediated cytotoxicity had no effect on antigen-specific proliferation. Those sugars that did suppress antigen-induced proliferation had no effect on PHA-induced proliferation. Furthermore, some of these sugars only inhibited if they were added at the initiation of the assay; they failed to inhibit if added 24 hr after the initiation of the assay. Antigen-pulsing experiments suggested that these sugars did not block antigen uptake by human monocytes. These data suggest that a variety of cellular interactions may be mediated by receptors with specificity for simple sugars. The ability to block these naturally occurring lectins specifically both in vitro and in vivo may prove to be a powerful tool for dissecting out various forms of cellular recognition and collaboration.

Fructokinase I of pea seeds has been purified to homogeneity and the enzyme shown to be monomeric, with a molecular weight of 72,000 +/- 4000. The reaction mechanism was investigated by means of initial velocity studies. Both substrates inhibited the enzyme; the inhibition caused by MgATP was linear-uncompetitive with respect to fructose whereas that caused by D-fructose was hyperbolic-noncompetitive against MgATP. The product D-fructose 6-phosphate caused hyperbolic-noncompetitive inhibition with respect to both substrates. MgADP caused noncompetitive inhibition, which gave intercept and slope replots that were linear with D-fructose but hyperbolic with MgATP. Free Mg2+ caused linear-uncompetitive inhibition when either substrate was varied. L-Sorbose and beta, gamma-methyleneadenosine 5'-triphosphate were used as analogs of D-fructose and MgATP, respectively. Inhibition experiments using these compounds indicated that substrate addition was steady-state ordered, with MgATP adding first. The product inhibition experiments were found to be consistent with a steady-state random release of products. The substrate inhibition caused by MgATP was most likely due to the formation of an enzyme-MgATP-product dead-end complex, whereas that caused by D-fructose was due to alternative pathways in the reaction mechanism. The inhibition caused by Mg2+ can be explained in terms of a dead-end complex with either a central complex or an enzyme-product complex.

L-sorbose, xylitol and sorbitol solutions (56 mM) were not hemolytic when incubated with erythrocytes of 30 healthy volunteers, 14 thalassemic heterozygotes and in 30 horses, 30 cows and 30 Osborne-Mendel rats. Lysis of dog erythrocytes was most pronounced when incubated with L-sorbose but was also significant in xylitol and sorbitol solutions.

Mono and oligosaccharides were used to inhibit the cytotoxicity of antisera detecting HLA-DRw antigens on monocytes isolated from peripheral blood. Certain sugars preferentially inhibited antisera detecting some DRw antigens and not others. Sera detecting HLA-A and B antigens were not inhibited with the sugars used. Anti-DRw sera blocked the attachment of radiolabeled sugars to monocytes with the same patterns as the reciprocal blocking of cytotoxicity by the sugars. The results were not consistent with the intrepretation that carbohydrates are an antigenic "component" of DRw specificity, but rather that the surface structures, possibly those bearing the DRw antigens, are receptors for mono and oligo saccharides.

Stimulated mixed saliva and interproximal plaque were exposed to the ketohexose sorbose. The average pH of an in vitro 1%-sorbose/saliva mixture increased with time when compared with a highly significant pH-decrease of a sucrose/saliva mixture. In contrast to sucrose rinses, the telemetrically recorded pH of interproximal plaque did not drop below pH 5.5 during and subsequent to rinsing with sorbose solutions.

Many carbohydrates play an important role in the process of absorption of several inorganic compounds, particularly of calcium, as shown by FOURNIER. VAUGHAN and FILER have proved that all carbohydrates are equally active under particular conditions: the difference of their action on calcium absorption is related to their absorption speed rate. Fructose appears in an intermediate situation between rapidly and slowly absorbed oses according to Cori's classification based on rates of absorption. In order to examine more closely the extent of differences of carbohydrates on calcium absorption, we chose to compare the action of free and combined fructose with that of carbohydrates found in normal feeding. Six months old rats in a state of calcium equilibrium received orally 2 ml aquous mixture containing 0,01 mM/ml calcium supplemented by 0,12 mu Ci 45 Ca and 0,075 mM/ml carbohydrate. The rats were divided into groups according to the carbohydrate they received, which was one of the following: D-glucose, D-mannose, D-fructose, L-sorbose, maltose, lactose, sucrose, starch, glycogen or inulin. Both absorption and retention of calcium were observed. A coefficient of absorption of 45Ca and the specific radioactivity of bone were established by the measurements of radioactivity of blood samples, which were taken 1 1/2 hour, 3 hours and 24 hours after ingestion, of intestinal content and feces, and of a femur after nitroperchloric mineralization. The results showed that values of absorption coefficient and of specific radioactivity are high for slowly absorbed sugars (mannose, sorbose, lactose) but are very low for free glucose or for glucose easily released by intestine enzymatic activity. Free fructose possesses in intermediate activity equivalent to that of inulin. However, sucrose administered at the same concentration has little effect on calcium absorption.

1. Growing rats were fed diets containing graded levels (0, 100, 200 and 300 g/kg diet) of sorbose for 6 weeks. Protein, fat and energy deposition were determined by carcass analysis. 2. The values for growth, serum insulin level, digestible energy (DE), metabolizable energy (ME) and fat and energy deposition declined with the increment of dietary sorbose. 3. The efficiency of protein utilization (protein retained/protein consumed) was hardly affected by dietary sorbose. The DE and ME of sorbose per se was calculated as 14.09 and 12.35 kJ/g respectively. The efficiency of energy utilization (energy retained/ME intake) decreased with the increase of dietary sorbose, although sorbose had an ME. 4. The relative weights of gastro-intestinal tract and liver were positively associated with dietary sorbose level, although the reverse was true for the amount of stomach content, being heavier with higher dietary sorbose. 5. It is suggested that dietary sorbose, as a sweetener as well as a bulky agent, seems to be a suitable sugar for the obese and diabetic with special reference to lower body fat and energy deposition without reducing protein utilization.

When observed over a temperature range, erythrocyte membrane lipids undergo a transition at 18-20 degrees C (Zimmer, G. and Schirmer, H. (1974) biochim. Biophys. Acta 345, 314-320). This observation has prompted an investigation of the effects that substrate binding has on the transition of the red cell membrane. Glucose and sorbose were compared, since transport kinetics of these sugars still pose unresolved questions. In membranes, preloaded with glucose, the break at the transition temperature was intensified, while it was abolished or reversed in membranes preloaded with sorbose. These results were corroborated using different solubilization procedures (sonication, sodium dodecyl sulfate treatment) of the membranes, and also different techniques (viscosimetry, 90 degrees light scattering, 1-anilino-naphthalene-8-sulfonate fluorescence). In extracted membrane lipids, viscosimetry indicated a break at transition temperature after preloading with either glucose or sorbose. Disc electrophoresis revealed a different binding pattern of the two sugars. It is suggested, that the amplification of the discontinuity in red cell membranes by glucose and the abolition or reversal of the break by sorbose are mediated by membrane protein- and/or membrane lipid-protein interaction.

Effect of n-pentyl glycosides and alkyl alpha-L-sorbopyranosides on IgE antibody formation in rats and mice were investigated. When n-pentyl alpha-L-sorbopyranoside was given subcutaneously or orally, the IgE antibody formation in rats and mice was suppressed, while no suppression of hemagglutinin formation was observed. The study on timing of administration indicated that n-pentyl alpha-L-sorbopyranoside significantly suppressed the secondary IgE antibody response when administered before the secondary immunization.

1. NAD(P)ase activity was stimulated when 1% sorbose was present in the culture medium of A. nidulans, and this effect was partially reversed by 1% glucose. 2. The level of extracellular NAD(P)ase was more affected by sorbose in the culture medium than the intracellular enzyme and no morphological changes were obtained. 3. The sorbose effect on NAD(P)ase activity appears to be specific since two other exoenzymes tested (beta-glucosidase and alkaline protease) show normal secretion patterns. 4. These findings suggest that the sorbose effect on NAD(P)ase production may be the consequence of metabolic disorders not necessarily linked with the morphological changes induced by the ketohexose.

Since the sweet ketohexose L-sorbose causes overt hemolysis in dogs but not in man, we examined the possibility that L-sorbose induces a "prehemolytic state" of human red cells, manifesting itself as impairment of rheological red cell properties. After 2 hours incubation at 37 degrees C relative viscosity of red cell suspensions measured by radial spreading in filter paper and packing ability of red cells were normal. Incubation for 24 and 48 hours of red cells in media containing L-sorbose, glucose or no sugar showed that relative viscosity was best maintained in glucose. Relative viscosity and packing ability of red cells in L-sorbose containing suspensions decreased less than in suspensions without sugar. This difference was independent of the glucose metabolism, red cell ATP, osmolality and pH of the suspending media, but appeared to be related to different degrees of spheroechinocytic red cell shape transformation observed in different suspending media. It is possible that L-sorbose has some antiechinocytic properties and/or that it induces an alteration of red cell membrane flexibility. There is no indication of an L-sorbose induced "prehemolytic state" in human red cells.

Sorbose at 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0% levels, sodium-desoxycholate at 0.025, 0.050, 0.075, 0.1 and 0.125% levels, and griseofulvin at 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, and 0.010% levels restrict the growth of colonies of Chaetomium aureum, both at pH 6.5 and 7.0. Restriction of colonies was most effective with 0.7% sorbose, 0.1% sodium-desoxycholate, and 0.006% griseofulvin in the medium adjusted to pH 6.5. Surface tension activity of sorbose, sodium-desoxycholate, and griseofulvin in different concentrations was determined, following the usual standard method.