[28] Methods for the assessment of peptide precursors. Studies on insulin biosynthesis

Publisher Summary The discovery of proinsulin, the biosynthetic precursor of insulin, has stimulated a search for the existence of precursors of other polypeptides. Growing evidence suggests that such forms exist not only for many peptide hormones including, along with insulin, parathyroid hormone, glucagon, and gastrin, but also for structural proteins including collagen, and virus capsule proteins. It is difficult to provide specific methods for the identification and analysis of all polypeptide precursors because of the divergent origin and chemical properties of the possible forms. The approach in each ease must consist of an imaginative synthesis of currently available methods for detecting and separating related proteins. A critical assessment of the precursor–product relationship of any pair of polypeptides requires both biochemical and chemical approaches. The methods used for the determination of this relationship and for the final characterization of the precursor form are largely those traditionally used in the detection and isolation of a variety of proteins and peptides. The final proof for the existence of a precursor polypeptide must rely on several carefully met criteria, each of which may only be suggestive in the absence of the others.