REGULATION OF GLYCOLYSIS IN TETANIZED CAT SKELETAL MUSCLE IN SITU.

Abstract : The effect of tetanic stimulation on the concentrations of metabolites in cat gastrocnemius muscle in situ was studied. Glucose-6-phosphate and fructose-6-phosphate accumulated as much as twentyfold, whereas changes in other glycolytic intermediates were less marked. The level of creatine-phosphate decreased 50% in 30 sec of tetanus. The concentrations of high energy adenine nucleotides, ATP, ADP, and AMP, were constant. From changes in relative specific activities of the intracellular glucose and glucose-6-phosphate pools it was concluded that, during the greatly enhanced rate of metabolism concomitant with the stimulation, over 90% of the glucosyl-carbon entering glycolysis was derived from glycogen by the phosphorylase reaction. The findings are in accord with the view that the phosphorylase and phosphofructokinase reactions are the major loci of glycolytic control in mammalian skeletal muscle. The results specifically exclude a suggested rate-limiting role for the phosphohexose-isomerase reaction, which was found to be at, or near, equilibrium in the resting and the tetanic muscle, even through the glycolytic flux increased greatly during stimulation. (Author)