Characterization of Isoenzymes of Adenosine Triphosphate: D-Hexose 6-Phosphotransferase from Rat Liver<sup>*</sup>

González, Carmen; Ureta, Tito; Babul, Jorge; Rabajille, Eliana; Niemeyer, Hermann M.

doi:10.1021/bi00854a014

Cited by 65 publications

(22 citation statements)

References 28 publications

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“…The K,-deGlc of 63mM resembles closely the K,-deGlc of glucokinase of rabbit liver (55 mM [13]) and of rat liver (95 mM [I41 ; 40 mM [15]). There is aggreement among all authors that the K m values for deGlc are three t o five times higher than those for glucose.…”

Section: Discussionmentioning

confidence: 76%

Occurrence and Function of a High‐K_m Hexokinase in Immature Red Blood Cells

Gerber

Schultze

Rapoport

1970

European Journal of Biochemistry

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The formation of 14C0, from [ l-14C]glucose and [6-14C]glucose by reticulocytes of rabbit and rat is dependent on the concentration of glucose over a wide range, indicating reactions preceding the formation of glucose-6-phosphate to be dependent on glucose concentration.I n haemolysates of rabbit reticulocytes a high-Km hexokinase was demonstrated by its kinetic properties. It corresponds to the glucokinase of liver. This enzyme does not occur in mature red blood cells of man and rabbit, nor in reticulocytes of newlyborns with erythro-blastosis fetalis. The presence of glucokinase in reticulocytes introduces a metabolic path of glucose utilization which is not subject to regulation by the phosphofructokinase.

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Section: Discussionmentioning

confidence: 76%

Occurrence and Function of a High‐K_m Hexokinase in Immature Red Blood Cells

Gerber

Schultze

Rapoport

1970

European Journal of Biochemistry

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“…N-acetylglucosamine (NAG), mannoheptulose (MH), the regulatory protein, and palmitoyl CoA act on glucokinase as competitive inhibitors with respect to glucose (12, [25][26][27]. Because several of the mutant proteins that we produced had a modified affinity for glucose, it was important to test the inhibitory effect of these compounds at equivalent concentrations of glucose.…”

Section: E Ffect On the Affinity For Competitive Inhibitorsmentioning

confidence: 99%

Study of the regulatory properties of glucokinase by site-directed mutagenesis: conversion of glucokinase to an enzyme with high affinity for glucose.

2000

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To identify the amino acids involved in the specific regulatory properties of glucokinase, and particularly its low affinity for glucose, mutants of the human islet enzyme have been prepared, in which glucokinase-specific residues have been replaced. Two mutations increased the affinity for glucose by twofold (K296M) and sixfold (Y214A), the latter also decreasing the Hill c o e fficient from 1.75 to 1.2 with minimal change in the a ffinity for AT P. Combining these two mutations with N166R resulted in a 50-fold decrease in the half-saturating substrate concentration (S 0 . 5 ) value, which became then comparable to the K m of hexokinase II. The location of N166, Y214, and K296 in the three-dimensional structure of glucokinase suggests that these mutations act by favoring closure of the catalytic cleft. As a rule, mutations changed the affinity for glucose and for the competitive inhibitor mannoheptulose (MH) in parallel, whereas they barely affected the affinity for N-acetylglucosamine (NAG). These and other results suggest that NAG and MH bind to the same site but to d i fferent conformations of glucokinase. A small reduction in the affinity for the regulatory protein was observed with mutations of residues on the smaller domain and in the hinge region, confirming the bipartite nature of the binding site for the regulatory protein. The K296M mutant was found to have a threefold decreased affinity for palmitoyl CoA; this effect was additive to that previously observed for the E279Q mutant, indicating that the binding site for long-chain acyl CoAs is located on the upper face of the larger domain. D i a b e t e s 4 9 :1 9 5-201, 2000

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“…Three of the hexokinases (A, B, and C) display high affinity for glucose and are often referred to as low-K, hexokinases or simply hexokinases; the fourth (hexokinase D) was found to exhibit a high Km for glucose and is commonly called "glucokinase" (EC 2.7.1.2). This discovery was soon followed by the search of several other tissues in various mammalian species for their content of hexokinase isozymes and by the study of the main kinetic properties of the isozymes (4)(5)(6). In the case of the rat intestinal mucosa, several reports differ with respect to the number and nature of isozymes present (3,(7)(8)(9)(10)(11).…”

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confidence: 99%

Kinetic, chromatographic and electrophoretic studies on glucose-phosphorylating enzymes of rat intestinal mucosa

Vera

Cárdenas

Niemeyer

1984

Archives of Biochemistry and Biophysics

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The number and nature of glucose-phosphorylating enzymes of rat intestinal mucosa were investigated by chromatographic, electrophoretic, and kinetic methods. Three fractions with glucose-phosphorylating activity were obtained from the supernatant fluid of mucosa homogenate by means of DEAE-cellulose chromatography, corresponding to hexokinases A and B (EC 2.'7.1.1.), and N-acetyl-D-glucosamine kinase (EC 2.7.1.59). Although the latter uses N-acetylglucosamine as the main substrate, it is also able to phosphorylate glucose. Electrophoresis in polyacrylamide and in cellulose acetate gels showed the same three enzyme activities. None of these procedures revealed the presence of either hexokinase D ("glucokinase") or hexokinase C in the intestinal mucosa. In the sediment fractions hexokinase A and B, but not N-acetylglucosamine kinase, were found. The K, values for glucose of partially purified hexokinases A and B were 0.025 and 0.174 mM, respectively, and their substrate specificity was the same as that of hexokinases A or B from other tissues. Partially purified N-acetylglucosamine kinase showed hyperbolic saturation functions for N-acetylglucosamine and ATP, with Km values of 0.021 and 0.38 mM, respectively. This enzyme also phosphorylated glucose, mannose, fructose, 2-deoxyglucose, and glucosamine. The dependence of velocity on glucose concentrations was complex, mimicking negative cooperativity. The molecular weight of both hexokinases A and B was 98,000 and that of N-acetylglucosamine kinase was 59,000. The kinetic properties, as well as the chromatographic and electrophoretic mobilities, of N-acetylglucosamine kinase may serve to confuse it with hexokinase D, and thus several criteria should be applied for correct identification.Rat liver contains four hexokinase isozymes (ATP:D-hexose-6-phosphotransferase, EC 2.7.1.1) which were separated by DEAE-cellulose chromatography and were named A, B, C, and D, according to their order of elution (1).

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Characterization of Isoenzymes of Adenosine Triphosphate: D-Hexose 6-Phosphotransferase from Rat Liver^*

Cited by 65 publications

References 28 publications

Occurrence and Function of a High‐K_m Hexokinase in Immature Red Blood Cells

Occurrence and Function of a High‐K_m Hexokinase in Immature Red Blood Cells

Study of the regulatory properties of glucokinase by site-directed mutagenesis: conversion of glucokinase to an enzyme with high affinity for glucose.

Kinetic, chromatographic and electrophoretic studies on glucose-phosphorylating enzymes of rat intestinal mucosa

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Characterization of Isoenzymes of Adenosine Triphosphate: D-Hexose 6-Phosphotransferase from Rat Liver*

Cited by 65 publications

References 28 publications

Occurrence and Function of a High‐Km Hexokinase in Immature Red Blood Cells

Occurrence and Function of a High‐Km Hexokinase in Immature Red Blood Cells

Study of the regulatory properties of glucokinase by site-directed mutagenesis: conversion of glucokinase to an enzyme with high affinity for glucose.

Kinetic, chromatographic and electrophoretic studies on glucose-phosphorylating enzymes of rat intestinal mucosa

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Characterization of Isoenzymes of Adenosine Triphosphate: D-Hexose 6-Phosphotransferase from Rat Liver^*

Occurrence and Function of a High‐K_m Hexokinase in Immature Red Blood Cells

Occurrence and Function of a High‐K_m Hexokinase in Immature Red Blood Cells