Intracellular Compartmentation of Glycolytic Phosphate Esters

Rat diaphragm was incubated with [14C]-glucose or [14C]-pyruvate; a number of the phosphorylated glycolytic intermediates were then isolated and their specific activities determined. Following incubation with either substrate, the specific activities of fructose 6-phosphate, fructose 1,6-diphosphate, and phosphoenolpyruvate were very close to that of the substrate. The specific activities of glucose 6-phosphate and phosphoglyceric acids were much lower than those of the substrates and of their immediate precursors; their relative specific activities were different for the two substrates. It is concluded that there are multiple intracellular pools of glucose 6-phosphate and phosphoglyceric acids and that the pools involved in glycolysis are distinct from those involved in gluconeogenesis. Insulin had no effect on the pattern of specific activities.