C-peptide is cleaved from proinsulin, stored in secretory granules, and eventually released into the bloodstream in amounts equimolar with those of insulin. The measurement of the C-peptide is an important test for the β-cell function. In the red blood cells of type 2 diabetic patients, Na+,K+ ATPase activity is strongly related to blood C-peptide levels. C-peptide signal transduction in human renal tubular cells involves the activation of phospholipase C and PKC-δ and PKC-varepsilon, as well as RhoA, followed by phosphorylation of ERK1/2 and JNK and a parallel activation of Akt. C-peptide shows specific binding to a G-protein-coupled membrane binding site, resulting in Ca2+ influx, activation of mitogen-activated protein kinase signalling pathways and stimulation of Na+, K+ ATPase and endothelial nitric oxide synthase.
Wahren, J. et al. Am. J. Physiol. Endocrinol. Metab. 278, E759 (2000); Zhong, Z. et al. Diabetologia 48, 187 (2005); Van Cauter, E. et al. Diabetes 41, 368 (1992); Vague, P. et al. Exp. Diabesity Res. 5, 37 (2004).
Sequence (One-Letter Code)
Sequence (Three-Letter Code)
H - Glu - Ala - Glu - Asp - Leu - Gln - Val - Gly - Gln - Val - Glu - Leu - Gly - Gly - Gly - Pro - Gly - Ala - Gly - Ser - Leu - Gln - Pro - Leu - Ala - Leu - Glu - Gly - Ser - Leu - Gln - OH