RADIOACTIVE PHOSPHORUS STUDIES ON HEXOSEMONOPHOSPHATE METABOLISM IN RESTING MUSCLE

Abstract

Radioactive P has been used to study the metabolism of glucose- and fructose-6-phosphates in the resting metabolism of striated muscle of cats and frogs. In the muscles of frogs, but not in those of cats, the 2 phosphorylated sugars are directly interconvertible. In the muscles of cats, but not those of frogs, there is ready interchange of phosphate groups, either direct or indirect, between fructose-6-phosphate and adenosine triphosphate. Neither in cats nor in frogs is there any interchange of phosphate groups between glucose-6-phosphate and adenosine triphosphate. In fasted cats, the adm. of phosphate leads to a mobilization of glucose-6-phosphate on the muscle cell membrane. The adm. of glucose to fasted cats increases markedly the phosphate-induced mobilization of glucose-6-phosphate on the muscle cell membrane. Phosphate doea not lead to a mobilization of glucose-6-phosphate on the cell membrane of cats in the post-absorptive state, nor doea glucose adm. to such animals evoke such mobilization. Evidence is presented that the absorption of glucose by the muscle cell takes place through the formation of glucose-6-phosphate on the cell membrane, penetration of the glucose portion of this molecule through the membrane, followed by hydrolysis of the phosphate linkage, with the phosphate remaining in the extracellular phase. In resting muscle, absorption of glucose aparently takes place only when the carbohydrate reserves have been depleted, as by fasting.