Proinsulin and the Biosynthesis of Insulin

THE protein hormone insulin seems to be of perennial interest to biochemists. It was among the first to be crystallized and was the first protein whose primary structure was elucidated by Sanger and his collaborators in the 1950's (Fig. 1). It is also the first protein that was totally synthesized chemically, this feat having been accomplished in 1964 in several laboratories throughout the world. Much interest has centered around the mechanism of biosynthesis of its two-chain structure. Two major possibilities exist: the two polypeptide chains might be made on separate ribosomal units and then combined through the formation of disulfide . . .