C-peptide is not present in mature insulin and during maturation...then when is it present?During synthesis?

What is the major role of C-peptide?

C-peptide,also called as connecting peptide  is a short 31-amino-acid protein that connects insulin  A-chain to its B-chain in the pro insulin molecule. Pro insulin is synthesized in the endoplasmic reticulum, where it is folded and its disulfide bonds  are oxidized. After pro insulin is packaged into vesicles in the Golgi apparatus, the C-peptide will be  removed, leaving the A-chain and B-chain, bound together by disulfide bonds, which becomes the insulin molecule

C peptide – It is a type of blood test that helps to detect whether the diabetes is type 1 or type 2.It serves as a linkbetween the A- and the B- chains of insulin and facilitates the efficient assembly, folding, and processing of insulin in the endoplasmic reticulum.