Glycolytic Control Mechanisms

Abstract

A detailed kinetic analysis of the changes of the glycolytic intermediates has been made in the main electric organ of Electrophorus electricus during periods of electrical discharge and recovery.Discharge of the organ was elicited by electrical stimulation and was associated with a transient increase in the levels of the glycolytic intermediates and the utilization of endogenous ATP and creatine phosphate.The high energy reserves were partially replenished during recovery by increased glycolytic activity.Principal sites of control in the glycoIytic pathway were identified at phosphoxylase and phosphofructokinase.Glycogen utilization was induced by a prompt increase in the active form of phosphorylase b kinase.Increases of phosphorylase (I and glucose-l-P followed in turn after a brief delay, The increased rate of input of hexose phosphates to the glycolytic pathway was accommodated by concurrent activation of phosphofructokinase, and the levels of glucose-6-P and fructose-6-P either remained approximately constant or diminished while fructose-1,6-di-P levels increased greatly.The activated glycolytic flux was subsequently switched off by inhibition of phosphofructokinase, as evidenced by increases in the levels of glucose-6-P and fructose-6-P and a decrease in the level of fructose-l.,6-di-P.Glycogenolysis was cm-tailed by the reconversion of phosphorylase II to phosphorylase b.The kinetics of the metabolic changes during different times of discharge indicate that phosphorylase and phosphofructokinase are regulated by separate mechanisms.