An electrophoretic study of the distribution and properties of human hexokinases

Molecular effects of Vitamin-D and PUFAs metabolism in skeletal muscle combating Type-II diabetes mellitus

Multiple post-receptor intracellular alterations such as impaired glucose transfer, glucose phosphorylation, decreased glucose oxidation, and glycogen production contribute to insulin resistance (IR) in skeletal muscle, manifested by diminished insulin-stimulated glucose uptake. Type-2 diabetes mellites (T2DM) has caused by IR, which is also seen in obese patients and those with metabolic syndrome. The Vitamin-D receptor (VDR) and poly unsaturated fatty acids (PUFAs) roles in skeletal muscle growth, shapes, and function for combating type-2 diabetes have been clarified throughout this research. VDR and PUFAs appears to show a variety of effects on skeletal muscle, in addition it shows a promising role on bone and mineral homeostasis. Individuals having T2DM are reported to suffer from severe muscular weakness and alterations in shape of the muscle. Several studies have investigated the effect on VDR on muscular strength and mass, which leads to Vitamin-D deficiency (VDD) in individuals, in which most commonly seen in elderly. VDR has been shown to affect skeletal cellular proliferation, intracellular calcium handling, as well as genomic activity in a variety of different ways such as muscle metabolism, insulin sensitivity, which is the major characteristic pathogenesis for IR in combating T2DM. The identified VDR gene polymorphisms are ApaI, TaqI, FokI, and BsmI that are associated with T2DM. This review collates informations on the mechanisms by which VDR activation takes place in skeletal muscles. Despite the significant breakthroughs made in recent decades, various studies show that IR affects VDR and PUFAs metabolism in skeletal muscle. Therefore, this review collates the data to show the role of VDR and PUFAs in the skeletal muscles to combat T2DM.

Identification, expression and bioactivity of hexokinase in amphioxus: insights into evolution of vertebrate hexokinase genes

Hexokinase family includes hexokinases I, II, III and IV, that catalyze the phosphorylation of glucose to produce glucose 6-phosphate. Hexokinase IV, also known as glucokinase, is only half size of the other types of hexokinases that contain two hexokinase domains. Despite the enormous progress in the study of hexokinases, the evolutionary relationship between glucokinase and other hexokinases is still uncertain, and the molecular processes leading to the emergence of hexokinases in vertebrates remain controversial. Here we clearly demonstrated the presence of a single hexokinase-like gene in the amphioxus Branchiostoma japonicum, Bjhk, which shows a tissue-specific expression pattern, with the most abundant expression in the hepatic caecum, testis and ovary. The phylogenetic and synteny analyses both reveal that BjHK is the archetype of vertebrate hexokinases IV, i.e. glucokinases. We also found for the first time that recombinant BjHK showed functional enzyme activity resembling vertebrate hexokinases I, II, III and IV. In addition, a native glucokinase activity was detected in the hepatic caecum. Finally, glucokinase activity in the hepatic caecum was markedly reduced by fasting, whereas it was considerably increased by feeding. Altogether, these suggest that Bjhk represents the archetype of glucokinases, from which vertebrate hexokinase gene family was evolved by gene duplication, and that the hepatic caecum plays a role in the control of glucose homeostasis in amphioxus, in favor of the notion that the hepatic caecum is a tissue homologous to liver.

Pathogenesis of insulin resistance in skeletal muscle

Insulin resistance in skeletal muscle is manifested by decreased insulin-stimulated glucose uptake and results from impaired insulin signaling and multiple post-receptor intracellular defects including impaired glucose transport, glucose phosphorylation, and reduced glucose oxidation and glycogen synthesis. Insulin resistance is a core defect in type 2 diabetes, it is also associated with obesity and the metabolic syndrome. Dysregulation of fatty acid metabolism plays a pivotal role in the pathogenesis of insulin resistance in skeletal muscle. Recent studies have reported a mitochondrial defect in oxidative phosphorylation in skeletal muscle in variety of insulin resistant states. In this review, we summarize the cellular and molecular defects that contribute to the development of insulin resistance in skeletal muscle.

Molecular evolution of the vertebrate hexokinase gene family: Identification of a conserved fifth vertebrate hexokinase gene

Hexokinases (HK) phosphorylate sugar immediately upon its entry into cells allowing these sugars to be metabolized. A total of four hexokinases have been characterized in a diversity of vertebrates-HKI, HKII, HKIII, and HKIV. HKIV is often called glucokinase (GCK) and has half the molecular weight of the other hexokinases, as it only has one hexokinase domain, while other vertebrate HKs have two. Differing hypothesis has been proposed to explain the diversification of the hexokinase gene family. We used a genomic approach to characterize hexokinase genes in a diverse array of vertebrate species and close relatives. Surprisingly we identified a fifth hexokinase-like gene, HKDC1 that exists and is expressed in diverse vertebrates. Analysis of the amino acid sequence of HKDC1 suggests that it may function as a hexokinase. To understand the evolution of the vertebrate hexokinase gene family we established a phylogeny of the hexokinase domain in all of the vertebrate hexokinase genes, as well as hexokinase genes from close relatives of the vertebrates. Our phylogeny demonstrates that duplication of the hexokinase domain, yielding a HK with two hexokinase domains, occurred prior to the diversification of the hexokinase gene family. We also establish that GCK evolved from a two hexokinase domain-containing gene, but has lost its N-terminal hexokinase domain. We also show that parallel changes in enzymatic function of HKI and HKIII have occurred.

Pathogenesis of type 2 diabetes mellitus

This article provides an overview of the pathogenesis of type 2 diabetes mellitus. Discussion begins by describing normal glucose homeostasis and ingestion of a typical meal and then discusses glucose homeostasis in diabetes. Topics covered include insulin secretion in type 2 diabetes mellitus and insulin resistance, the site of insulin resistance, the interaction between insulin sensitivity and secretion, the role of adipocytes in the pathogenesis of type 2 diabetes, cellular mechanisms of insulin resistance including glucose transport and phosphorylation, glycogen and synthesis,glucose and oxidation, glycolysis, and insulin signaling.

Hexokinase isozyme distribution in human skeletal muscle

Two isoforms of hexokinase (type I and type II) are expressed in skeletal muscle; however, the intracellular distribution of these hexokinase isoforms in human skeletal muscle is unclear. The current study was undertaken to assess this issue because binding of hexokinase to subcellular structures is considered to be an important mechanism in the regulation of glucose phosphorylation. Vastus lateralis muscle was obtained from healthy lean individuals. Muscle homogenate was separated at 45,000g into particulate and cytosolic fractions. The activity and subcellular distribution of hexokinase isozymes in human skeletal muscle was determined using ion-exchange chromatography and a highly sensitive high-performance liquid chromatography-based hexokinase assay. This criterion method was used to validate a modified thermal inactivation method for distinguishing type I and type II isoforms. Mean hexokinase activity was 3.88 +/- 0.65 U/g wet wt or 0.64 +/- 0.11 U/mU creatine kinase (CrK) in the particulate fraction and 0.45 +/- 0.22 U/g wet wt or 0.07 +/- 0.03 U/mU CrK in the cytosolic fraction. Hexokinase I and II accounted for 70-75 and 25-30% of total hexokinase activity, respectively. Nearly all (95%) of hexokinase I activity (0.52 +/- 0.09 U/mU CrK) was found in the particulate fraction, consistent with the known high affinity of hexokinase I for mitochondria. Hexokinase II activity was also largely bound to the particulate fraction (72%), but 28% was found within the cytosolic fraction. Thus, within the particulate fraction, the relative contributions of hexokinase I and hexokinase II were 81 and 19%, whereas within the cytosolic fraction, the relative contributions for hexokinase I and hexokinase II were 37 and 63%.

Impaired activity and gene expression of hexokinase II in muscle from non-insulin-dependent diabetes mellitus patients

After entering the muscle cell, glucose is immediately and irreversibly phosphorylated to glucose-6-phosphate by hexokinases (HK) I and II. Previous studies in rodents have shown that HKII may be the dominant HK in skeletal muscle. Reduced insulin-stimulated glucose uptake and reduced glucose-6-phosphate concentrations in muscle have been found in non-insulin-dependent diabetes mellitus (NIDDM) patients when examined during a hyperglycemic hyperinsulinemic clamp. These findings [correction of finding] are consistent with a defect in glucose transport and/or phosphorylation. In the present study comprising 29 NIDDM patients and 25 matched controls, we tested the hypothesis that HKII activity and gene expression are impaired in vastus lateralis muscle of NIDDM patients when examined in the fasting state. HKII activity in a supernatant of muscle extract accounted for 28 +/- 5% in NIDDM patients and 40 +/- 5% in controls (P = 0.08) of total muscle HK activity when measured at a glucose media of 0.11 mmol/liter and 31 +/- 4 and 47 +/- 7% (P = 0.02) when measured at 0.11 mmol/liter of glucose. HKII mRNA, HKII immunoreactive protein level, and HKII activity were significantly decreased in NIDDM patients (P < 0.0001, P = 0.03, and P = 0.02, respectively) together with significantly decreased glycogen synthase mRNA level and total glycogen synthase activity (P = 0.02 and P = 0.02, respectively). In the entire study population HKII activity estimated at 0.11 and 11.0 mM glucose was inversely correlated with fasting plasma glucose concentrations (r = -0.45, P = 0.004; r = -0.54, P < 0.0001, respectively) and fasting plasma nonesterified fatty acid concentrations (r = -0.46, P = 0.003; r = -0.37, P = 0.02, respectively). In conclusion, NIDDM patients are characterized by a reduced activity and a reduced gene expression of HKII in muscle which may be secondary to the metabolic peturbations. HKII contributes with about one-third of total HK activity in a supernatant of human vastus lateralis muscle.

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.

Purification and physical properties of hexokinase from human erythrocytes

A bulk purification is described for hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) from human erythrocytes. Following a 110,000-fold purification from 40 litres of blood, 5 mg protein with a specific activity of 22 units/mg were obtained. On application of various separation techniques, the enzyme activity co-migrated with the main protein component. The physical properties, such as the relative molecular mass of 108,000 and sedimentation coefficient of 5.5 S, are similar to those of the enzyme from human heart. In particular, there is a correspondence in the conformational response to glucose 6-phosphate as shown by an association of the enzyme promoted by this metabolite.

Enzyme activities of cultured erythroblasts

The enzyme activities of cultured early erythroid progenitor cells (burst-forming unit erythroid, BFU-E) were measured and were compared with the activities of mature erythrocytes. The enzyme activity of acetylcholinesterase was not detectable in the erythroblasts. The ratios of phosphofructokinase and glutathione peroxidase were low due to low enzyme activities in both the erythroblasts and erythrocytes. The ratios of triose phosphate isomerase, phosphoglycerate kinase, and adenylate kinase were low due to high enzyme activities in both the erythroblasts and erythrocytes. The ratios of hexokinase, glucose phosphate isomerase, monophosphoglyceromutase, pyruvate kinase, and adenosine deaminase were high due to high enzyme activities in the erythroblasts. The isozyme of erythroblast hexokinase was of the prototype isozyme I, while pyruvate kinase was predominantly of the prototype M2, with two hybrid isozymes to the anodal side by electrophoresis. These facts suggest that there is a greatly different metabolic pattern during the maturation of the erythroid cells.

Isolation and glucose-6-phosphate-mediated dimerization of hexokinase from human heart

Soluble hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1) was purified from human heart. 1 kg of tissue provided 25 mg hexokinase with a specific activity of 58 units/mg, representing a 1700-fold purification and 47% yield. The purification involved six steps, including affinity chromatography with glucosamine attached to Sepharose. The material was homogeneous according to electrophoresis, gel-filtration and sedimentation in the ultracentrifuge, but gave two main components on electrophoresis in denaturing conditions. From determination of the sedimentation and diffusion coefficients, the relative molecular mass was calculated to be 105 000. The enzyme is monomeric, but glucose 6-phosphate promotes an association to dimers. This effect is reversible and is independent of the concentrations of glucose or inorganic phosphate. The results support the postulate that soluble and mitochondrion-bound hexokinases are identical.

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.

Electrophoretically detectable mutations induced in CHO cells by varying doses of ultraviolet radiation

Chinese hamster ovary (CHO) cells were subjected to ultraviolet radiation (UV) at doses resulting in 100% (no irradiation), 50-30%, 20-10% and approximately 1% survival. 2 divisions after UV exposure surviving cells were cloned and clones expanded for electrophoretic analysis of the products of approximately 40 enzyme loci. 4 different classes of variants (electrophoretic shifts, nulls, enzyme re-expression and enzyme modification) were detected in 29 of 1329 clones analyzed and proven mutants by subclone analysis. The frequency of mutants in the irradiated groups (28/38391 loci screened or 7.3 X 10(-4) was significantly higher than controls. The frequency of shift mutants at 10-20% survival was higher than shifts at 30-50% survival and was significantly higher than shifts at approximately 1% survival. The frequency of nulls increased with dose. 12 of the 28 mutants obtained in the irradiated groups were at only 3 of the mean 41 loci screened/clone. These results indicated that shift mutants could be detected more efficiently than nulls at lower dose and that loci varied widely with respect to their susceptibility to UV mutagenesis. Multiple null mutants at 2 loci, isocitrate dehydrogenase 2 and hexokinase 2, indicated they may be hemizygous in CHO cells.

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.

A survey on the formation and localization of secondary isozymes in mammalia

A survey on the formation of secondary isozymes (= multiple molecular forms of enzymes) is given by means of well-documented enzyme systems. Further examples of a certain type of formation are summarized in tabular form. Eight different classes of enzyme variants deriving from translational processes are discussed. These are: aggregation, polymerization, oxidation and reduction of free SH groups, limited proteolysis, cleavage of carbohydrate residues, deamidation, noncovalent binding of coenzymes, and conformational isomerism. In addition, the intracellular distribution of secondary isozymes is discussed, as are the formation of artificial enzyme variants and the recognition of multiple enzyme forms caused by an exchange of neutral amino acids. About 200 original papers are cited. The reference list was completed in early 1979.

Isoelectric focusing of hexokinase and glucose-6-phosphate dehydrogenase isoenzymes in erythrocytes of newborn infants and adults

Isoenzymes of glucose-6-phosphate dehydrogenase and hexokinase from red cells of newborn infants were analysed by isoelectric focusing in polyacrylamide gel after partial purification. The pattern of isoenzyme distribution was compared with that of erythrocytes from adults. Glucose-6-phosphate dehydrogenase isoenzyme distribution was identical between erythrocytes from newborn infants and adults. Erythrocytic hexokinase isoenzymes patterns were different between newborn infants and adults. Erythrocytes from adults contain a hexokinase isoenzyme which has the same isoelectric point as rat liver hexokinase isoenzyme I (pH 6 . 01). This isoenzyme is lacking in red cells from newborn infants. Isoenzymes with the isoelectric properties of rat liver isoenzyme II (pH 5 . 48) were not detectable in red cells from adults, nor from newborn infants. The occurrence of an isoenzyme III in red cells remained unclear, because only a faint staining was observed in the corresponding region of erythrocytic gels. Preliminary results revealed a fetal type of hexokinase isoenzyme distribution in infants with an age of 10 months. This indicates that regulation of the synthesis of Hb F and of fetal hexokinase isoenzymes is not correlated.

Hexokinase isozyme distribution and regulatory properties in lymphoid cells

The glycolytic enzyme hexokinase is studied in cultured leukemic lymphoblasts, in normal lymphocytes and in lymphoblasts obtained by stimulation of normal lymphocytes with phytohaemagglutinin. Hexokinase activity levels in cultured lymphoblasts and in normal lymphocytes are identical, but somewhat higher levels are found in stimulated lymphocytes. Cultured leukemic lymphoblasts differ in isozyme content in comparison to the other lymphoid cells. Besides hexokinase I, which is detected in all the lymphoid cells, they are characterized by the presence of hexokinase II. The concentration of type II increases during cell growth. Another difference between leukemic lymphoblasts and mature and stimulated lymphocytes is found in the regulatory properties of hexokinase I. Hexokinase I from both normal and stimulated lymphocytes is inhibited by glucose-1,6-diphosphate. This inhibition is decreased in part by addition of inorganic phosphate. Hexokinase I from leukemic lymphocytes, however, is inhibited to a lesser extent by glucose-1,6-diphosphate. Inorganic phosphate has no effect at all on this inhibition. In accordance with these findings a different pattern in the hexokinase I region was detected in electrophoresis with several cell types. The subisozyme hexokinase Ib, which appears to be the phosphate-regulated form, is predominant in lymphocytes, whereas it is present in a minor fraction in the cultured leukemic lymphoblasts. In these cells hexokinase Ic predominates.

Hexokinase deficiency in erythrocytes: a new variant in 5 members of a Finnish family

15 cases of congenital haemolytic anaemia have thus far been attributed to hexokinase (HK) deficiency in erythrocytes. We report some clinical, biochemical and genetic findings from 5 members of a Finnish family with this deficiency. The proband, a 1-year-old girl, was the only patient with anaemia. All subjects had either mild or marked reticulocytosis. Red cell ATP levels were at the lower range of normal in all subjects and 2,3-DPG was abnormally low in one. The activities of red cell enzymes, other than HK, were within or above the normal range, respectively. The Km-values for glucose and fructose were elevated (ATP normal) in the subjects with HK deficiency. We speculate that the family represents heterozygosity of a mutant allele and that there is phenotypic variation associated with the HK mutant. The locus might be subject to mutations which lead to a variety of HK variants and to a spectrum of diseases. This point of view is in accordance with the overwhelming variation of reaction kinetics and metabolic effects of this and other reported cases.

Relationship between glucose phosphorylating activities and erythrocyte age

Glucose phosphorylating activity of human erythrocytes quickly decreases during cell ageing; the electrophoretic pattern suggests that this fast decrease is due mainly to the isozyme II. We have shown that in the young cells only hexokinase I and II are responsible for the glucose phosphorylation, while in the old cells another glucose phosphorylating activity, more evident at high glucose concentration, is also present. The appearance of this activity during cell ageing could be interpreted as a post-translational modification of the native hexokinase.

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.

An examination of the age-related patterns of decay of acid phosphatase (ACP1) in human red cells from individuals of different phenotypes

A study has been made of the decay of acid phosphatase (ACP1) in the human red cell using red cell fractions of different mean ages prepared by density gradient centrifugation. Red cells from acid phosphatase type A and type B individuals were used in the study. Acid phosphatase activity of the red cell fractions was determined by two different assay methods. The results obtained were comparable and have been combined. Acid phosphatase type A and type B showed a biphasic decay pattern with a rapid early loss of activity, followed by a more gradual rate of decline. Type A appeared to decay more rapidly than type B in both decay phases. It is proposed that differences in stability between type A and type B in vivo may explain the observed differences in activity between the enzyme types. There was no evidence for the generation of secondary isozymes by acid phosphatase type A or type B during red cell aging.

Comparative studies on red blood cell glucose phosphorylating activities of mammals

1. ATP-D-hexose-6-phosphotransferase activity was measured in red blood cells of man, rabbit, pig and cow. Mean values ranged from 0.60 to 1.06 units/g haemoglobin and no significant difference was obtained with different glucose concentrations. 2. The characteristics of glucose phosphorylating activities in red blood cells of the species studied were similar. 3. Chromatography on DEAE column revealed two different glucose phosphorylating activities in red cells of man, rabbit and pig, and only one in cow red cells. 4. The first hexokinase activity is the predominant form and is saturated with low glucose concentrations; the second is noticeably marked at high glucose concentrations.

Properties of human erythrocyte hexokinase related to cell age

The kinetic, electrophoretic and immunological properties of hexokinase from human erythrocytes have been studied in relation to cell age. No differences in kinetic behaviour between hexokinase partly purified from reticulocytes, 10% youngest cells, normal red cell population or from 10% oldest cells were observed. The stability of the enzyme preparations showed little differences; hexokinase from the 10% youngest cells was the most labile enzyme, followed respectively by the enzyme from reticulocytes, normal red cell population and the 10% oldest cells. The electrophoretic pattern of erythrocyte hexokinase changed during senescence. The hexokinase activity located in the second band from the anode is shifted to the third with increasing cell age. The molecular specific acitivity of the enzyme from the 10% youngest cells, the normal red cell population and the 10% oldest cells remains the same, while the molecular specific activity of hexokinase from reticulocytes was much lower.

An investigation of the products of 53 gene loci in three species of wild Canidae: Canis lupus, Canis latrans, and Canis familiaris

This article describes an investigation of inter- and intraspecific variation in three small populations of wild Canidae-wolf, coyote, and dingo. The products of 53 gene loci were examined. Very little interspecies variation was observed, but the level of intraspecific variation was compatible with that found in man.

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.