Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.1 (hexokinase)
 5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

As previously reported, during rabbit red blood cell aging glucose phosphorylating activities show several modifications. In the first period of the red cell life span the predominant form is similar to hexokinase II, while in the mature erythrocyte the predominant glucose phosphorylating activity resembles hexokinase I. In the oldest cells glucose phosphorylating activity has a low affinity (high Km) for glucose. In this paper the modifications of hexokinase in cell aging have been studied in vivo in a young erythrocyte population synchronized by actinomycin D, and in vitro in red cells separated in fractions according to different ages. Since protein synthesis is lacking in the mature red cell, we are inclined to explain the presence of low-affinity hexokinase activity in the oldest erythrocytes as an age-dependent transformation of a primary hexokinase.
 ...
PMID:Decay pattern of rabbit erythrocyte hexokinase in cell aging. 4 84

Kinetic and structural studies have been carried out of two isoenzymes of hexokinase from the rat, hexokinase II and glucokinase. Although both enzymes are monomeric, hexokinase II has a molecular weight double that of glucokinase and resembles a dimer of glucokinase. The co-operativity of glucokinase, which is not observed for hexokinase II, appears to be kinetic in origin rather than the consequence of ineractions between distinct glucose-binding sites.
 ...
PMID:Mammalian hexokinases: a system for the study of co-operativity in monomeric enzymes. 55 44

Administration of L-thyroxine into intact rats caused a distinct increase in the activity of hexokinase in liver tissue. In the isoenzyme spectrum of hexokinase the activity of hexokinase II was increased significantly. After repeated administration of insulin, liver tissue cells lost their capacity to respond to the hormone administration by induction of hexokinase. Administration of L-thyroxine into animals caused a distinct increase in the hexokinase activity in liver tissue. In isoenzyme spectrum of hexokinase under effect of L-thyroxine a significant increase in the hexokinase II activity was also observed.
 ...
PMID:[Effect of L-thyroxine on the activity and isoenzymatic spectrum of liver hexokinase in intact and insulin-resistant rats]. 113 5

The effect of insulin on the intracellular localization of rat skeletal muscle hexokinase isozyme II (hexokinase II) was studied in vivo. It was found that after injection of the hormone the glucose concentration in the muscle gradually increases in parallel with the hexokinase II redistribution between the cytosol and the mitochondrial fraction in the direction of the bound form of the enzyme. This effect of insulin is due to glucose, an indispensable participant of the complex formation between the enzyme and the mitochondrial membrane. It was shown that the effect of glucose as a hexokinase II adsorbing reagent is a highly specific one. The hexokinase II binding to mitochondria in the presence of glucose is accompanied by changes in some kinetic properties of the enzyme. A kinetic analysis of catalytic efficiency of the free and bound hexokinase II forms revealed that the catalytic efficiency of hexokinase II within the composition of the enzyme-membrane complex exceeds by two orders of magnitude that of the free enzyme. The data obtained are discussed in the framework of an adsorption mechanism of hexokinase activity regulation in the cell.
 ...
PMID:[The effect of insulin on the catalytic efficacy of rat skeletal muscle hexokinase isoenzyme II]. 174 17

An up to 14-fold increase in total hexokinase activity induced by low-frequency stimulation in rat fast-twitch muscle was followed by a rapid decay in enzyme activity after cessation of stimulation. In vivo labeling revealed that these alterations were related to rapid changes in [35S]methionine incorporation into hexokinase II. A recovery period of 15 h after cessation of stimulation was sufficient to normalize the approximately 30-fold elevated [35S]methionine incorporation.
 ...
PMID:Rapid up- and down-regulation of hexokinase II in rat skeletal muscle in response to altered contractile activity. 231 60

Increased contractile activity as induced by chronic low-frequency stimulation evoked in rat fast-twitch muscle an almost immediate increase in the ratio between structure-bound and free hexokinase. In addition, an up to 14-fold rise in total hexokinase activity occurred after two weeks of stimulation indicating that glucose phosphorylation became a limiting step of glucose utilization under these conditions. The increase in hexokinase activity was transitory as prolonged stimulation led to a leveling off and steep decline with an apparent half-life of 2.5 days after three weeks of stimulation. The transient increase in glucose phosphorylating capacity can be explained by previous observations indicating that prolonged stimulation leads to a shift from a carbohydrate-based to a fatty-acid-based energy metabolism. Using an isozyme-specific sandwich ELISA, it was shown that both increases and decreases in total hexokinase activity were matched by corresponding changes in the amount of hexokinase isozyme II protein. Increases in both total hexokinase activity (3-4-fold) and hexokinase II protein content were also observed after denervation in rat fast-twitch muscle. In view of reports in the literature, it is suggested that the elevations in hexokinase II observed with increased contractile activity and denervation relate to enhanced glucose uptake and utilization.
 ...
PMID:Changes in free and bound forms and total amount of hexokinase isozyme II of rat muscle in response to contractile activity. 237 6

Saccharomyces cerevisiae mutants containing different point mutations in the HXK2 gene were used to study the relationship between phosphorylation by hexokinase II and glucose repression in yeast cells. Mutants showing different levels of hexokinase activity were examined for the degree of glucose repression as indicated by the levels of invertase activity. The levels of hexokinase activity and invertase activity showed a strong inverse correlation, with a few exceptions attributable to very unstable hexokinase II proteins. The in vivo hexokinase II activity was determined by measuring growth rates, using fructose as a carbon source. This in vivo hexokinase II activity was similarly inversely correlated with invertase activity. Several hxk2 alleles were transferred to multicopy plasmids to study the effects of increasing the amounts of mutant proteins. The cells that contained the multicopy plasmids exhibited less invertase and more hexokinase activity, further strengthening the correlation. These results strongly support the hypothesis that the phosphorylation activity of hexokinase II is correlated with glucose repression.
 ...
PMID:The residual enzymatic phosphorylation activity of hexokinase II mutants is correlated with glucose repression in Saccharomyces cerevisiae. 268 72

Several hundred new mutations in the gene (HXK2) encoding hexokinase II of Saccharomyces cerevisiae were isolated, and a subset of them was mapped, resulting in a fine-structure genetic map. Among the mutations that were sequenced, 35 were independent missense mutations. The mutations were obtained by mutagenesis of cloned HXK2 DNA carried on a low-copy-number plasmid vector and screened for a number of different phenotypes in yeast strains bearing chromosomal hxk1 and hxk2 null mutations. Some of these mutants were characterized both in vivo and in vitro; they displayed a wide spectrum of residual hexokinase activities, as indicated by three assays: in vitro enzyme activity, ability to grow on glucose and fructose, and ability to repress invertase production when growing on glucose. Of those that failed to support growth on fructose, only a small minority made normal-size, stable, and inactive protein. Analysis of the amino acid changes in these mutants in light of the crystallographically determined three-dimensional structure of hexokinase II suggests important roles in structure or catalysis for six amino acid residues, only two of which are near the active site.
 ...
PMID:Isolation and characterization of mutations in the HXK2 gene of Saccharomyces cerevisiae. 268 71

Significance of the binding of hexokinase to mitochondria was examined with respect to stabilization of the enzyme by the binding. Stability during the incubation of the mitochondria-bound forms of hexokinases I and II, both prepared from Ehrlich-Lettre ascites hyperdiploid tumor cells (ELD cells), were compared with that of the corresponding free forms. During the incubation at pH 7.4 and 37 degrees C up to 60 min, hexokinase activities decreased gradually, and the decrease in the activity of the free form was much more marked than that of the bound form for both hexokinases. Hexokinase II was much less stable than I, and the activity of the free form of the former was almost lost by the incubation for 15 min. But, more than a half of the original activity of hexokinase II was retained even after 60 min of the incubation when the enzyme was bound to mitochondria. Addition of 50 mM glucose increased the stability of hexokinase II, but the stabilizing effect was less marked for hexokinase I. On the other hand, addition of 28 mg/ml of bovine serum albumin markedly stabilized hexokinase I to almost the same extent as was observed with mitochondria. On the contrary, the serum albumin had little stabilizing effect on hexokinase II. These findings indicate that the binding to mitochondria stabilizes the hexokinases of ELD cells, though the stability is different by nature between hexokinases I and II.
 ...
PMID:Stabilization of hexokinases I and II of ELD cells by binding to mitochondria. 271 12

The relative rate of synthesis of hexokinase II in the skeletal muscle of the normal, streptozotocin-diabetic, and diabetic insulin-treated rat was determined by the rate of incorporation of [3H]leucine into hexokinase II and the total cytosolic proteins to determine if the rate of hexokinase II synthesis was altered relative to that of the average protein. This relative rate of synthesis of hexokinase II is approximately 1.9 times higher in the normal than in the diabetic rat. The administration of insulin to the diabetic animal increases the rate of hexokinase synthesis to approximately normal levels. An enzyme-linked immunosorbent assay procedure was developed to determine the amount of hexokinase II protein in the skeletal muscle extracts, and immunoprecipitation was utilized to determine the hexokinase II activity. The specific activity of hexokinase II was determined from these analyses. The specific activity of hexokinase II was the same in the skeletal muscle extracts from normal, streptozotocin-diabetic, and diabetic insulin-treated rats. These results suggest that the decrease in muscle hexokinase activity is not caused by the loss of an activator of the enzyme nor by the increased formation of a hexokinase inhibitor in streptozotocin-induced diabetes; rather the decrease in hexokinase II activity reported in diabetic rats relative to normal animals is a result of decreased synthesis coupled to increased degradation in the diabetic relative to the normal animal.
 ...
PMID:Effect of streptozotocin-induced diabetes and insulin treatment on the synthesis of hexokinase II in the skeletal muscle of the rat. 294 26


1 2 3 4 5 6 7 Next >>