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Hexokinase of white adipose tissue

1963; Elsevier BV; Volume: 67; Linguagem: Inglês

10.1016/0006-3002(63)91827-4

1878-2434

David L. DiPietro,

Cancer, Hypoxia, and Metabolism

Apparent Michaelis constants for glucose and fructose of white adipose tissue hexokinase have been estimated by determining the rate of hexose C-1 oxidation through the hexose monophosphate shunt with added glucose-6-P dehydrogenase and NADP+. The values obtained are: fructose, 3 mM; glucose, 0.07 mM. It is likely that a single enzyme catalyzes the phosphorylation of glucose and fructose since a summation of reaction rates is not observed in the presence of both sugars. Glucose competitively inhibits fructose phosphorylation although the presence of fructose has little or no effect on glucose phosphorylation. This observation is in keeping with the relative affinities of the enzyme for the two hexoses. The enzyme displays a specific requirement for ATP and is activated both by magnesium and manganese ions. Under the experimental conditions described, glucose phosphorylation rates of between 30 and 60 μmoles/min/g of adipose tissue nitrogen were observed.