Genetically determined polymorphism of a form of hexokinase, HK III, found in human leucocytes

A rare genetically determined electrophoretic variant of human leucocyte type III hexokinase

Various lines of evidence from starch gel electrophoretic experiments demonstrate the existence of a genetically determined rare variant form of the type III isozyme of hexokinase (HK) in the leucocytes of a small percentage of the general human population. This enzymatically active variant (designated IIIS) migrates slightly, but significantly, slower than the common form (designated IIIF). In addition to finding various individuals with a two-banded pattern (heterozygotes containing both IIIS and IIIF), a finding reported previously by S. Povey, G. Corney, and H. Harris ((1975) Ann. Hum. Genet. 38, 407-415), we discovered one person homozygous for the variant phenotype. In close agreement with Povey et al., screening of 59 individuals at random indicated a gene frequency of about 0.017 for the IIIS allele, corresponding to a homozygous genotype for this allele that would be expected in about one of every 3500 individuals. Experiments involving the mixing of blood samples from the individual homozygous for IIIS with those homozygous for IIIF indicate that secondary in vitro changes, a possibility suggested by Povey et al., are not responsible for the appearance of the variant. This conclusion was supported by a demonstration of the specificity of the alteration in type III's mobility in comparison with the lack of alterations in any of the LDH isozymes, glucose-6-phosphate dehydrogenase, and various amido black-stainable proteins. These studies confirm the proposal for a genetically determined polymorphism of type III HK. No differences could be found between the total HK activity (according to spectrophotometric assays) of extracts from the subject homozygous for the variant and the activity from the homozygote for the common form, in terms of either their Km values for glucose or their heat stability properties. The similarity of Km values was supported by kinetic assays performed during staining of the individual forms on electrophoretic gels. Previous findings, reported elsewhere, of type III HK in RBC extracts were shown here to be attributable to contamination, by leucocytes, of the extracts. As a consequence of these studies, slight, but significant, amounts of type II-like HK were also discovered in leucocytes. Because our studies described above were completed in 1969, advantage was taken of the opportunity to test the HK pattern 17 years later from some of the same subjects. The patterns of the homozygotes for IIIS and for IIIF and the heterozygotes were found to be identical to the original ones, indicating no age-, environmental-, or other time-related changes that could explain the variation in type III HK.

Isoenzyme pattern and subcellular localization of hexokinases in human breast cancer and nonpathological breast tissue

Subcellular distribution of hexokinase (HK) isoenzymes in 22 human breast cancers (21 primary cancers and 1 axillary metastatic growth) and 7 non-pathological human mammary gland tissue samples was studied with starch gel electrophoresis on isolated cell fractions obtained by differential centrifugation. Fractions used were cytosol, mitochondria and microsomes. A comparison of two methods for detecting HK activity was made, yielding different results regarding HK II and HK III. A method based on the ability of NADPH to fluoresce in UV gave a constant pattern of HK isoenzymes. In non-pathological breast tissue, only HK I was seen, i.e. in the cytosol and the microsomal fractions. HK I was also seen in all fractions of the cancers, but another more anodal band of HK I, as well as HK II and HK III, consistently appeared in the cytosol fractions. The more commonly used staining technique with tetrazolium dye revealed HK II in 45% and HK III in 50% of the samples. The pattern of HK isoenzymes in the cancers was the same irrespective of estrogen and progesterone cytosolic receptor contents and the histology of the tumors. The fluorescence method is, therefore, much more sensitive than the tetrazolium technique for detecting HK activity after electrophoresis and could explain difference in results obtained by various laboratories.

Genetic analysis of human lymphocyte proteins by two-dimensional gel electrophoresis: 4. Genetic polymorphism of cytosol 100k polypeptide

We describe a genetic polymorphism of a human cellular polypeptide with mol. wt. 100,000, detected in peripheral blood lymphocytes by high resolution two-dimensional electrophoresis. Three different electrophoretic types (1-1, 2-1, and 2-2) of the polypeptide have been identified. Family and population studies indicate that the three phenotypes of the polypeptide are determined by two common alleles at a single autosomal locus. The polypeptide occurs in the cytosol and is one of the abundant polypeptides of B-lymphoblastoid cells, T-lymphoblastoid cells, fibroblasts, and HeLa cells. The data indicate that the cytosol polypeptide with mol. wt. 100,000 shows a genetic polymorphism determined by a new autosomal locus. It is proposed that the polypeptide and its locus be temporarily designated cytosol 100k polypeptide (C100k polypeptide) and C100P, respectively. In a Japanese population, the gene frequencies of C100P1 and C100P2 were 0.907 and 0.093, respectively.

Separation and characterization of hexokinase I subtypes from human erythrocytes

Hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1) type 1 from human erythrocytes exists in four electrophoretical distinct forms, termed Ia, Ib, Ic and Id in order of their increasing anodal electrophoretic mobility at pH 8.8. We were able to separate type Ia, Ib and Icd on phosphocellulose by using a discontinuous gradient elution. The three chromatographically distinct forms do not differ in their affinity constants for the substrates glucose and MgATP2-. In addition the inhibition by glucose 1,6-diphosphate does not differ significantly for all forms. However, the regulation of these inhibitions by inorganic phosphate is much less for type Ia compared to the other subtypes (P = 0.001). Aging of the red cells is accompanied by a relative increase of the proportion of type Ic and Ia, which is the less regulated form of the enzyme. This shift in electrophoretic and regulatory properties is argued to be due to a post-translational modification of the primary enzyme.

Changes in the activity and isozyme patterns of glycolytic enzymes during stimulation of normal human lymphocytes with phytohaemagglutinin

A study has been made of the effects of phytohaemagglutinin on the gene expression of the glycolytic enzymes in cultured human lymphocytes. All the enzymes were found to show an average increase in activity of between 160% and 360% in stimulated cells, but the increases were greater for the enzymes comprising the second half of the pathway. The enzyme activities in stimulated cells, cultured for 72 h, were similar to the activities measured in long-term lymphoid lines. Starch-gel electrophoresis was used to examine the isozyme patterns of the enzymes before and after exposure of the lymphocytes to PHA. Six of the enzymes showed isozyme patterns unchanged by stimulation. Four of the enzymes, aldolase, triosephosphate isomerase, enolase and lactate dehydrogenase, showed different isozyme patterns in stimulated cells from those seen in uncultured or unstimulated cells. The electrophoretic results showed a good correlation in isozyme pattern between uncultured lymphocytes and cultured unstimulated lymphocytes, and between PHA-stimulated lymphocytes and long-term lymphoid lines.

Comparison of type I hexokinases from pig heart and kinetic evaluation of the effects of inhibitors

Type I hexokinase (ATP:D-hexose 6-phospotransferase, EC 2.7.1.1) of porcine heart exists in two chromatographically distinct forms. These do not differ significantly in size, electrophoretic mobility at pH 8.6 or kinetic properties. Both forms obey a sequential mechanism and are potently inhibited by glucose 6-phosphate. In contrast to observations of type I hexokinase from brain, inhibition by glucose 6-phosphate is not relieved by inorganic phosphate. Under most conditions, low concentrations of phosphate (less than 10 mM) have little effect on the kinetic behaviour of the enzyme but at higher concentrations this ligand is an inhibitor. Mannose 6-phosphate inhibits in a manner analogous to glucose 6-phosphate but the Ki is much greater. In view of the similarity of the kinetic parameters governing phosphorylation of mannose and glucose, this difference in affinity for the inhibitor site is seen as consistent with the existence of a separate regulatory site on the enzyme. MgADP inhibits hexokinase but behaves as a normal product inhibitor and inhibition is competitive with respect to MgATP and non-competitive with respect to glucose.

Hexokinase isozymes of normal human subcutaneous adipose tissue

The isozymes of hexokinase in surgical specimens of human subcutaneous adipose tissue were separated by elution from DEAE-cellulose with linear KCl gradients at ph 7.4. Two peaks of activity were found: Peak 1 eluted at 0.05M KCl, and Peak 2 at 0.19M KCl. Michaelis constants (Km) for glucose were: Peak 1, 6.5 x 10-5M; Peak 2, 1.5 x 10-4M. Peak 2 was more susceptible than Peak 1 to inactivation by trypsin, 0.1 mg/ml, and was protected by 0.1M glucose. Both peaks were protected from heat inactivation (45 degrees) by 0.1M glucose. Peak 2 comprised 66 +/- 5 percent of the total hexokinase activity. No activity with the characteristics of hexokinase III was detected in human fat. In all these characteristics, the isozymes of human adipose tissue closely resemble hexokinases I and II from rats.

Purification and some properties of human erythrocyte hexokinase

1. Human erythrocyte hexokinase (ADP:D-hexose 6-phosphotransferase, EC 2.7.1.1) was purified 50 000--100 000-fold with a final specific activity of about 25--50 units/mg protein using gel-filtration, ion-exchange chromatography and affinity chromagraphy. 2. After isoelectrofocusing ofthe preparation one major protein band could be detected besides a minor band. THe isoelectric point of the major protein band was found to be 4.7. 3. After purification the enzyme could be stabilized in a medium containing inorganic phosphate, glucose, glycerol and mercaptoethanol. 4. The molecular weight was determined by gel-filtration and was found to be 132 000+/-8000. 5. The enzyme shows a broad pH optimum ranging from 7.0 to 8.4. 6. The kinetic behavior of the purified enzyme at 37 degrees C was somewhat different from the normal Michaelis-Menten kinetics due to its instability. The affinity constants were 0.048--0.080 mM for glucose and 0.57--1.0 mM for Mg-ATP. 7. The enzyme was specific for Mg- ATP as the nucleotide substrate. Mg-UTP, Mg-ITP,Mg-GTP and Mg-CTP were not converted to corresponding diphosphates. Several hexoses could be phosphorylated by the enzyme. Mannose could be phosphorylated at the same rate as glucose, although the affinity for the enzyme was lower (5m=0.60mM). Much lower rates and lower affinities were found with 2-deoxy-D-glucose (5m=1.0mM), D(+)-glucosamine (5m=4.5 mM) and fructose (5m=10 mM). N-acetyl-D-glucosamine , galactose andsorbose were not phosphorylated at all.

An examination of the age-related patterns of decay of the hexokinases of human red cells

A previous method for red cell fractionation by density gradient centrifugation, using a swing-out rotor, has been scaled up to deal with larger volumes of red cells. This method, involving the use of a zonal rotor, is described and has been applied to the study of the decay of hexokinase in the red cells of normal individuals. Hexokinase activity was seen to fall very rapidly in the young cells followed by a much more gradual decline in older cells. It is estimated that the mature red cell probably contains no more than 2-3% of the hexokinase activity originally present in the reticulocyte. An electrophoretic study showed a changing pattern of the isozymes HK1 and HK2 with increasing cell age. HK2 declines very rapidly in the early fractions whereas HK1 appears to decay more gradually.

An electrophoretic study of the distribution and properties of human hexokinases

An electrophoretic system which gives a clear separation of human hexokinases HK1, HK2 and HK3 is described. The distribution of the hexokinase isozymes in various human tissues, both adult and fetal, is reported. Some properties of the isozymes were investigated. HK2 was found to be more thermolabile than HK1, and there was also a small but significant difference in molecular size. Unlike HK3, HK1 and HK2 are not inhibited by high glucose concentrations. Screening of red cell lysates from 800 unrelated European individuals revealed no genetic variants of HK1 and HK2. However, in view of their difference in properties, it seems probable that the HK1 and HK2 isozymes are determined by separate gene loci.

Sub-unit structure of soluble and mitochondrial malic enzyme: demonstration of human mitochondrial enzyme in human-mouse hybrids

1. Malic enzyme has been examined by starch-gel electrophoresis in human cultured fibroblasts and in 60 brain samples. The polymorphism of MEM has been confirmed and the electrophoretic pattern suggests that this enzyme, like MES, is a tetramer. 2. The appearance of the soluble and mitochondrial malic enzymes in mouse and Chinese hamster is described, and the identity of the enzymes in man, mouse and hamster has been established from a study of interspecific somatic cell hybrids. In man and in hamster MES migrates anodal to MEM, whereas in the mouse MES is relatively less anodal than MEM. 3. Segregation of human enzymes in human--mouse and human--hamster somatic cell hybrids confirms the synteny of MES and PGM3. Data from human--mouse hybrids suggest that MEM is probably not syntenic with MES is probably not syntenic with MES in man, nor is it syntenic with GPI.