Proinsulin

Proinsulin is the single-chain biosynthetic precursor of insulin, as demonstrated by several convincing lines of evidence. The proteolytic conversion of proinsulin to insulin probably occurs early in the formation of insulin storage granules in the β-cells of the pancreas. When glucose is administered, some proinsulin appears to be released into the circulation concomitantly with insulin, but the significance of the finding is not known. The possible implications of proinsulin in the etiology of diabetes have not yet been fully explored.