Intracellular cleavage of protein and polypeptide precursors is now recognized as a widely occurring biosynthetk: mechanism. As this field has developed, proinsulin and its cleavage patterns and secretory products have served as useful models for investigations of other systems. A particularly relevant aspect of the proprotein concept is the simple mechanism it provides for the coordinate synthesis and discharge of related peptides from endocrine or other secretory cells. This report reviews briefly the role of the proinsulin C-peptide, first in terms of its special biosynthetk: functions, which are unique to the assembly of the two-chain insulin structure, and then with regard to its more general implications for other biosynthetk and secretory systems.

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