<prompt> C-peptide is seenIn Pre-proinsulinIn ProinsulinAs a gastrointestinal proactive moleculeAs a combined entity with insulin after secretion  <response>: Insulin Insulin is synthesized in the rough endoplasmic reticulum of the B cells The gene for insulin is located on the sho arm of chromosome 11 in humans. Normally, 90-97 of the product released from the B cells is insulin along with equimolar amounts of C peptide. C peptide can be measured by radioimmunoassay, it is an index of B cell function in patients receiving exogenous insulin. Ref:- Ganongs Review of Medical Physiology 25th ed; pg num:- 431 