Kinetic Mechanism of Activation of Muscle Glycogen Phosphorylase b by Adenosine 5′-Monophosphate

Abstract

The kinetic analysis of the enzymatic reaction catalyzed by glycogen phosphorylase b from the rabbit skeletal muscle has been carried out in the direction of glycogen synthesis under the conditions of the saturation of the enzyme by glycogen. The applicability of 12 different variants of the Monod-Wyman-Changeux model and 6 kinetic schemes involving the interaction of AMP- and glucose-1-phosphate-binding sites in the dimeric enzyme molecule is considered. The kinetic model has been proposed, which assumes (i) the independent binding of AMP and one molecule of glucose 1-phosphate with the enzyme saturated by glycogen, (ii) the exclusive binding of the second molecule of glucose 1-phosphate by the enzyme containing two molecules of AMP and one molecule of glucose 1-phosphate, and (iii) the exclusive ability of the complex of the enzyme with glycogen, two molecules of AMP, and two molecules of glucose 1-phosphate to undergo the catalytic transformation. The parameters of the equation of the initial steady-state rate of the enzymatic reaction are calculated by the nonlinear regression method. The proposed kinetic scheme is shown to satisfy to the following criteria: (i) the convergence under the regressional analysis, (ii) the reliability of the values of the parameters of the model, (iii) the minimality of the sum of the weighted squares of the differences between the experimental and calculated values of the reaction rate.