Insulin and Protein Metabolism

Abstract

The present status of protein synthesis within cells has been outlined. Protein is formed in the absence of insulin; the net formation of protein is accelerated by insulin. The effects of insulin on protein metabolism take place independently of the transport of glucose or amino acids into the cell; of glycogen synthesis; and of the stimulation of high energy phosphate formation. In the case of protein metabolism, as in certain studies on the pathways of glucose and fat metabolism, these observations reveal striking intracellular effects of insulin in many tissues. Within most tissues the effect of insulin appears to find expression predominantly at the microsomal level. Incidentally, other hormones which affect protein metabolism such as growth or sex hormones appear to act at the microsomes. The fact that insulin exerts effects on protein metabolism at other intracellular sites as well as the above independent effects leads one to agree that its action consists of a stimulation of multiple, seemingly unrelated, metabolic events. The fact that an immediate effect of insulin on protein synthesis is independent of the immediate need for extracellular glucose or amino acids does not mean that the sustained functioning of cells is likewise independent. The biochemist is fully aware of metabolic defects in diabetes which are not altered by insulin in vitro, but which demand varying periods of pretreatment of the animal. It is also known that in diabetes some proteins (enzymes) may be deficient while others may be produced in excess in the absence of insulin. It is suggested that the physician desires at least two kinds of relation between these fundamental studies and his patients. One is the possible relation of a deficiency of insulin action to pathological processes in tissues which have not as yet been examined by the methods described. The other is the need for more accurate measurements of the metabolic disorder and its control than such things as urinary and blood glucose. In developing such future improvements, the place of insulin in protein biosynthesis must be kept in mind.