THE SYNTHESIS OF PROTEINS IN VIVO

Abstract

Anabolism and catabolism. The study of metabolism, as pursued up to the present, is the study of catabolism. The contrast between the detailed chemistry of catabolism on the one hand, and the vague gen-eralisations with regard to anabolic processes on the other, stands out keenly, and in no group of substances is this so clearly seen as with the proteins. With the exception of the mode of action of pepsin, and to sume extent, the mechanism of deamination, it may be said that the study of protein catabolism has met with considerable success at all points; the hydrolysis to the amino-acids; the identification of these; the studies on proteolytic enzymes; ketolysis and ketogenesis; urea synthesis:-all these processes are more or less understood, and it is possible to trace in some detail, in normal conditions, a high percentage of protein nitrogen from one end of its course in the body to the other. What is known of the corresponding anabolic processes? Nitrogen, ingested in the form of protein, is laid down as protein in the tissues. The amino-acids are generally assumed to be the highest common factor in this change, and the anabolic process is regarded as the synthesis of body protein from the amino-acids traversing the walls of the intestinal canal. The only observations calculated to throw any light on this synthesis are those of Blackwood (1932) following the earlier work of Cary (1920, 1926) ; namely, that in the blood stream afferent to a site of protein synthesis, the amino-acids are in higher concentration than in the efferent. Catabolic processes are readily stimulated, initiated and controlled. Control of the anabolic processes is only through hormones of unknown action; protein synthesis can be stimulated by the administration of the anterior pituitary growth hormone, but this has, thus far, thrown n