Glucose as a regulator of glycogen phosphorylase in rat diaphragm: II. Effect of glucose and related compounds on phosphorylase phosphate

Abstract

1. 1. The mechanism by which glucose causes a decrease in phosphorylase a levels in isolated rat diaphragm was investigated. Although glucose is known to be an inhibitor of both phosphorylases a and b, the effect of glucose could not be explained by a direct inhibitory action of the hexose on these enzymes. In contrast, it has been found that glucose markedly activates phosphorylase phosphatase, thus decreasing the level of phosphorylase a. 2. 2. In addition to glucose, glycogen and Glc-6- P also enhanced phosphatase activity, while Fru-1,6- P 2 and P i were inhibitory. 3. 3. Possible mechanismsof glucose activation of diaphragm phosphorylase phosphatase were investigated. Results indicated that the observed effect cannot be explained by a change in the molecular form of the substrate, phosphprylase a. Glucose may alter the susceptibility of the substrate and/or its partially phosphorylated intermediates to phosphatase action. Alternatively, glucose may directly activate the phosphatase itself.