BIOSYNTHESIS OF POLYPEPTIDE HORMONES IN INTACT AND CELL-FREE SYSTEMS

Publisher Summary Since the discovery of proinsulin, post-translational modification of proteins by limited intracellular proteolysis has been recognized increasingly as a normal biosynthetic mechanism in the production of a wide variety of secretory, along with some viral, proteins. Little is known about the processing mechanisms involved, aside, in a few instances, from their tentative intracellular localization to the Golgi area, and some elements of their cleavage specificity. This chapter presents several interesting recent examples of pro-proteins and discusses the general significance of these formsMost small polypeptide hormones are derived via cleavage of larger precursor molecules. A number of examples are summarized; however, additional suggestive evidence of the existence of larger forms of somatostatin, pancreatic polypeptide, calcitonin, and vasopressin, as well as others is accumulating. These larger forms may fulfill a number of important functions in biosynthesis and secretion; however, a requirement for a minimum chain length of 65–70 residues for successful vectorial discharge and sequestration in the rough endoplasmic reticulum may provide an explanation for the existence of many of them.