[Kinetics behavior of isozymes I and II of rat skeletal muscle hexokinase after their binding to mitochondrial membranes].

Hexokinase from rat skeletal muscle hyaloplasm is represented by two isozymic forms I and II. The values of apparent Km (glucose) for these forms were calculated according to the Reiner method. After binding to mitochondrial membranes under effects of Mg2+ the value of V for hexokinase isozyme II is increased 3-fold, while its Km value is decreased 5 times; the properties of isozyme I remain thereby unchanged. After cessation of interaction with the membrane, under effect of ATP the free hexokinase reveals the same kinetic properties (V, Km, sensitivity to the inhibiting effect of glucose 6-phosphate) as does the native enzyme from hyaloplasm. The ability of hexokinase to exist in a bound or free state is also reversible and depends on the Mg2+/ATP ratio. The conditions for a reversible transfer of muscle hexokinase (isozymes I and II) from the hyaloplasm to the mitochondria-bound state completely coincide with those for cardiac enzyme (isozyme I). The data obtained are discussed in terms of a concept on an adsorption mechanism controlling the enzyme activity.