C-peptide is the connecting peptide removed when proinsulin is processed into mature insulin. Processing allows the insulin A and B chains to remain linked while the connecting segment is released. Endogenous secretion releases both products, but their circulating concentrations differ because their clearance differs. C-peptide measurements can therefore inform endogenous secretion, provided that the physiological and measurement context is considered. [ref]
Insulin Biosynthesis, Secretion, Structure, and Structure-Activity Relationships. proinsulin processing and C-peptide release
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