<p>This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.</p> <p>The C-peptide links the insulin A and B chains in proinsulin,
providing thereby a means to promote their efficient
folding and assembly in the endoplasmic reticulum during
insulin biosynthesis. It then facilitates the intracellular
transport, sorting, and proteolytic processing of proinsulin
into biologically active insulin in the maturing secretory
granules of the <italic>β</italic> cells. These manifold functions impose significant
constraints on the C-peptide structure that are conserved
in evolution. After cleavage of proinsulin, the intact
C-peptide is stored with insulin in the soluble phase of the
secretory granules and is subsequently released in equimolar
amounts with insulin, providing a useful independent
indicator of insulin secretion. This brief review highlights
many aspects of its roles in biosynthesis, as a prelude to
consideration of its possible additional role(s) as a physiologically
active peptide after its release with insulin into the
circulation in vivo.</p>
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Exp Diabesity Res. 2004; 5(1):7-14