Insulin and Protein Metabolism

Publisher Summary The evidence that the administration of insulin can induce growth in normal and hypophysectomized animals under certain conditions is discussed. At first sight it is insufficient to emphasize the importance of insulin in promoting protein biosynthesis. Experiments with isolated rat diaphragm show conclusively that the addition of insulin in vitro to the medium stimulates the incorporation into the protein of the diaphragm of radioactively labeled amino acids present in the medium. This stimulation occurs in the absence from the medium of added glucose, and the evidence available suggests that it in no way depends upon a primary action of insulin in enhancing the utilization of carbohydrate. Evidence is adduced to support the view that the rate of the incorporation of labeled amino acids into the protein of isolated diaphragm is a valid measure of protein biosynthesis. The mechanism of action of insulin in stimulating protein biosynthesis in muscle appears not to be in the translocation of amino acids across the cell membrane, but on a process more intimately concerned with the intracellular synthesis of protein. The possibility of the existence of a single point of action of insulin upon carbohydrate utilization, fat synthesis, and protein synthesis is discussed, and a unifying idea is tentatively put forward.