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The proband with lifelong hemolytic anemia has a high K0.5s phosphoenolypyruvate (PEP) erythrocyte pyruvate kinase (PK) variant substantially but incompletely normalized by the allosteric modifier fructose-1,6-diphosphate (F-1,6-P2) with conversion of sigmoidal to hyperbolic kinetics. Heterozygotes in four generations express qualitatively identical but less severely abnormal kinetics and lack overt hemolysis. Kinetic abnormalities are closely mimicked by sulfhydryl modification of normal PK. Three distinct clinical and metabolic phenotypes characterize the proband and two sisters: variant PK and hemolytic anemia, variant PK without clinical manifestations or hemolysis, and complete normality. Their mother, whose red cell PK is entirely normal except for a questionably slightly low Vmax, is postulated to express the gene products of nonidentical alleles, one encoding a product with mildly less favorable catalytic characteristics. At low PEP concentrations, the proband and heterozygotes for the PK mutant express only a very small fraction of normal PK activity despite apparent inheritance of one normal allele in the latter. Evidence suggests that disproportionately lowered PK activity may be a property of a heterotetrameric PK. Illusory abnormalities in nucleotide specificity are artifacts of diminished substrate affinity characterizing the mutant PK.

P1,P5-di(adenosine 5')pentaphosphate (Ap5A) is an excellent inhibitor of human hemolysate adenylate kinase at concentrations near 2 microM and above. At ten times this concentration and in hemolysate enzyme assays under conditions described in this paper it appears not to alter reaction data in the case of hexokinase, phosphofructokinase, and phosphoglycerokinase. In the pyruvate kinase assay, very modest reductions in activity are noted, and kinetics with phosphoenolpyruvate, adenosine diphosphate (ADP), and uridine diphosphate (UDP) are unaltered.

A child with chronic hemolytic anemia since birth was found to have erythrocyte pyruvate kinase (PK) in a highly unusual form relative to other mutant isozymes when characterized by International Committee for Standardization in Hematology criteria. Most properties of the partially purified isozyme (designated PK-Greenville) were altered minimally, if at all, except for nearly total insensitivity to allosteric activation by fructose-1,6-diphosphate (F-1,6-P). One parent appeared to be heterozygous for a null gene and the other for an allele governing production of the mutant isozyme. Apparent restriction of the molecular defect to ineffective activation kinetics suggests that the F-1,6-P binding site on erythrocyte PK is functionally as well as physically allosteric. The magnitude of the metabolic block at the PK step and the clinical severity indicate that allosteric modulation by F-1,6-P is a crucial property of PK in normal erythrocyte metabolism.

Studies of a Mexican kindred present evidence for a unique phenotype of erythrocyte glucosephosphate isomerase, GPI Valle Hermoso. The proband was apparently the homozygous recipient of a mutant autosomal allele governing production of an isozyme characterized by decreased activity, marked thermal instability, normal kinetics and pH optimum, and normal starch gel electrophoretic patterns. Unlike previously known cases, leukocyte and plasma GPI activities were unimpaired. This suggested that the structural alteration primarily induced enzyme instability without drastically curtailing catalytic effectiveness, thereby allowing compensation by cells capable of continued protein synthesis. Age-related losses of GPI, however, were not evident by density-gradient fractionation of affected erythrocytes.

Chronic hemolytic anemia in a 7-year-old Chinese boy was found to be associated with decreased activity of erythrocyte hexokinase (approximately 20% of appropriate control values). Alterations in kinetics, stability, pH optimum, or electrophoretic patterns could not be demonstrated with proband hexokinase, but subtle differences between maternal and paternal hexokinase characteristics suggested that two separate mutant isozymes were involved and that the proband was heterozygous for each. Comparisons with previously reported cases of hexokinase deficiency demonstrate the broad genetic heterogeneity that characterizes this disorder.

The concentrations of red cell CDP (dCDP)-choline and P-choline were measured and compared in normal subjects, in subjects with hemolytic anemia other than that due to pyrimidine-5'-nucleotidase deficiency, in homozygotes for the latter enzymopathy, and in a single subject with a hemolytic syndrome speculatively due to choline phosphotransferase deficiency.

Two subjects, not previously reported in detail, had severe inherited deficiencies of erythrocyte pyrimidine nucleotidase. This was manifested hematologically by moderate hemolytic anemia with splenomegaly, morphologically by punctate basophilic stippling of Wright's stained erythrocytes, and biochemically by intraerythrocytic accumulation of pyrimidine nucleotides, elevated concentrations of reduced glutathione, and partial deficiencies of ribosephosphate pyrophosphokinase. All 5 of their children were asymptomatic and phenotypically normal except for intermediate reductions in activities of pyrimidine nucleotidase consistent with heterozygosity for an autosomal recessive defect.

Enzymes of aerobic and anaerobic glycolysis, glutathione cycling, and nucleotide metabolism were assayed on erythrocytes from 7 healthy rhinoceroses, 2 rhinoceroses during periods of intravascular hemolysis, and 1 rhinoceros without clinical signs of illness, which was the mother of 3 offspring with intravascular hemolytic syndrome. Measurements also were made of erythrocyte concentrations of glycolytic intermediates, adenine nucleotides, and glutathione. Although comparison of results for healthy and affected rhinoceroses did not identify an enzyme abnormality as a cause for the hemolytic syndrome, the data provided information regarding the metabolic characteristics of erythrocytes from healthy rhinoceroses.

Erythrocytes from a patient with classical pyrimidine nucleotidase (PyN) deficiency had less than 10% residual PyN activity with uridine 5'-monophosphate (UMP) or cytidine 5'-monophosphate (CMP) as substrate, but exhibited brisk nucleotidase activity with thymidine 5'-monophosphate (dTMP). This strongly suggests the existence of separate enzymes or isozymes of PyN in normal human erythrocytes--an hypothesis that should be tested by similar studies in other cases of severe PyN deficiency, whether induced by genetic defects or lead toxicity.

A mutant erythrocyte isozyme of pyruvate kinase (PK) (ATP: pyruvate phosphotransferase, EC 2.7.1.40) has been found in associatin with chronic hemolytic anemia in two siblings who were doubly heterozygous for the isozyme and for quantitative PK deficiency of the usual form. The isozyme was characterized by approximately normal maximum reaction velocities but had markedly decreased affinity for the substrate, phosphoenolpyruvate (PEP), with 5-fold to 10-fold increases in half-saturation constants and decreased interaction between substrate binding sites. Two distinctly separable kinetic patterns for PEP were observed with multiple specimens. Concentrations of fructose 1,6-diphosphate (FDP) required for half-maximal activation were two orders of magnitude greater than controls, and optimal pH was lowered to 6.5. stability at 4 degrees C was markedly decreased, but the lost enzyme could be reactivated by fdp for periods even longer than normal controls.

The heterogeneity of pyruvate kinase (PK) deficiency associated with hereditary haemolytic anaemia is emphasized by studies of a kindred harbouring two distinct mutant forms of this enzyme, both of which were kinetically defective with markedly decreased affinities for the substrate, phosphoenolypyruvate. The two isoenzymes, designated PK-Vancouver1 and PK-Vancouver2, were primarily distinguishable from one another by differences in maximum in vitro activities and by variations in response to fructose-I,6-diphosphate activation. When combined in proband erythrocytes to the exclusion of any normal PK, the isoenzymes were associated with a severe chronic haemolytic process with many of the features of PK deficiency of the more common quantitative type. Clinical laboratory screening tests for detecting PK deficiency may be falsely negative or equivocal in such cases.

Pyruvate kinase was partially purified from erythrocytes of three unrelated, nonconsaguineous patients with chronic hemolytic anemia of differing clinical severities. Characterization of the defective PK isozymes by internationally standardized criteria indicated that one (PK-"Gainesville") had severely impaired substrate affinity, another (PK-"San Juan") had markedly reduced residual activity, and the third (PK-"Cape Canaveral") had a combination of milder defects. Each appears representative of subsets emerging from the heterogeneous molecular defects that make up pyruvate kinase deficiency.

A mutant isozyme of erythrocyte pyruvate kinase was found in a family of French-Canadian ancestry in association with hemolytic anemia. The isozyme was characterized by normal maximal activity, pH optimum, heat stability, and fructosediphosphate activation constants, but had markedly reduced affinity for the substrate, phosphoenolpyruvate. This kinetic defect was corrected almost entirely in vitro by low concentrations of fructosediphosphate.