[Interaction of isozymes I and II of hexokinase with a microsomal fraction of skeletal muscle of rats].

The conditions of reversible transition of hexokinase from the hyaloplasm to the rat skeletal muscle microsomal membranes were studied. The maximal absorption of the enzyme by the membranes was observed in the presence of Mg2+ and glucose at weakly alkaline values of pH. Adenyl nucleotides and glucose 6-phosphate taken at physiological concentrations at neutral and weakly acid values of pH make the effect of Mg2+ reversible. It was shown that the both hexokinase isozymes I and II localized in muscle hyaloplasm are capable of reversible transition from the free state to the bound one. All the effects observed during hexokinase interaction with the rough microsomal fraction occurred in the cases of a purified muscle sarcoplasmic reticulum fraction. The conditions for the enzyme interaction with the microsomal and mitochondrial membrane fractions were found to be practically identical. However, when the enzyme was bound to the microsomal membrane, some reversible changes (e. g. increase of V) took place; the Km value for glucose remained thereby unchanged. The data obtained are discussed in terms of an adsorption mechanism of hexokinase activity control in the cell.