Regulation of glycogen phosphorylase a phosphatase in Neurospora crassa

Abstract

1. 1. The active form of glycogen phosphorylase in crude mycelial extracts of Neurospora crassa can be inactivated by incubation of these extracts without any additions. F − prevents this transformation. 2. 2. Neurospora extracts catalyze the inactivation of rabbit muscle phosphorylase a. Using 32P-labeled preparations of muscle phosphorylase a, this activation follows a similar time course to 32P i liberation. 3. 3. The inactivation of phosphorylase a phosphate in mycelial extracts decreased the maximum velocity of the phosphorylase a to phosphorylase b conversion reaction when it was assayed at different phosphorylase a concentrations. 4. 4. Maximal phosphorylase a phosphatase activities were found between pH 7.6 and 8.3. Inactivation of the phosphorylase a phosphatase led to a decrease in the activity throughout the pH range tested. 5. 5. The incubation of mycelial preparations in the presence of ATP, ADP, AMP, GTP, CTP, UTP or pyrophosphate resulted in a time-dependent decrease in phosphorylase a phosphatase activity. 6. 6. Reactivation of an inactive phosphorylase a phosphatase from Neurospora mycelium was obtained by incubation with ATP and Mg 2+ plus and ATP-generating system. Kinetic studies of the phosphatase reactivation indicate that the reaction requires ATP-Mg 2+ and free Mg 2+. 7. 7. 3′, 5′-Cyclic AMP does not affect the rate of reactivation of the Neurospora phosphatase.