C-peptide is produced by the beta cells of the pancreas as part of the proinsulin molecule (insulin precursor). It initially connects (C-connecting) the A and B chains of proinsulin and is released when proinsulin is further processed into insulin. Originating from the same molecule, C-peptide and insulin are released into the blood stream in equal amounts. The half life of C-peptide (~30min) in blood is approximately 5 times that of insulin, which accounts for C-peptide levels occurring in greater amounts than insulin in sera. C-peptide is increased in type II diabetes and insulin resistance, in contrast to decreasing in type I diabetes. High levels of C-peptide levels can occur in insulin producing tumors.

Swiss-Prot Accession Number: P01308

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