[Determination of glycogen phosphorylase B activity by the turbidimetric method in the presence of the forward and reverse reaction substrates].

The turbidimetric method based on monitoring changes in the turbidity of glycogen solution at wavelengths above 300 nm has been developed for the measurement of catalytic activity of rabbit skeletal muscle glycogen phosphorylase B. The dependences of the initial rate of enzymatic reaction on molar ratio of inorganic phosphate in the inorganic phosphate-glucose-1-phosphate mixture have been obtained at various concentrations of the allosteric activator, AMP, or in the presence of inhibitors (D-glucose, glucose 6-phosphate). It has been shown that the changes in glycogen phosphorylase B activity in the presence of these modifiers are not affected by variations in the molar ratios of the substrate. A theoretical expression for the dependence of the initial rate of the reversible reaction S in equilibrium P catalyzed by the enzyme has been deduced as a function of the substrate (S) molar ratio.