Journal
EXPERIMENTAL DIABESITY RESEARCH
Volume 5, Issue 1, Pages 15-23Publisher
TAYLOR & FRANCIS INC
DOI: 10.1080/15438600490424479
Keywords
endothelial nitric oxide synthase; G protein coupled receptor; insulinomimetic effects; intracellular Ca2+; membrane binding; mitogen-activated protein kinase; Na+,K+ ATPase; proinsulin; regional blood flow
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New results present C-peptide as a biologically active peptide hormone in its own right. Although C-peptide is formed from proinsulin and cosecreted with insulin, it is a separate entity with biochemical and physiological characteristics that differ from those of insulin. There is direct evidence of stereospecific binding of C-peptide to a cell surface receptor, which is different from those for insulin and other related hormones. The C-peptide binding site is most likely a G-protein-coupled receptor. The association constant for C-peptide binding is approximately 3 x 10(9) M-1. Saturation of the binding occurs already at a concentration of about 1 nM, which explains why C-peptide effects are not observed in healthy subjects. Binding of C-peptide results in activation of Ca2+ and MAPK-dependent pathways and stimulation of Na+,K+-ATPase and eNOS activities. The latter 2 enzymes are both deficient in several tissues in type 1 diabetes. There is some evidence that C-peptide, and insulin may interact synergistically on the insulin signaling pathway. Clinical evidence suggests that replacement of C-peptide, together with regular insulin therapy, may be beneficial in patients with type I diabetes and serve to retard or prevent the development of long-term complications.
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