Proinsulin

insulin
Insulin undergoes extensive posttranslational modification along the production pathway. Production and secretion are largely independent; prepared insulin is stored awaiting secretion. Both C-peptide and mature insulin are biologically active. Cell components and proteins in this image are not to scale.
Identifiers
Symbol	INS
NCBI gene	3630
HGNC	6081
OMIM	176730
RefSeq	NM_000207
UniProt	P01308
Other data
Locus	Chr. 11 p15.5
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Proinsulin is the prohormone precursor to insulin made in the beta cells of the Pancreatic Islets, specialized regions of the pancreas. In humans, proinsulin is encoded by the INS gene.^[1][2] The pancreatic islets only secrete between 1% and 3% of proinsulin intact.^[3] However, because proinsulin has a longer half life than insulin, it can account for anywhere from 5–30% of the insulin-like structures circulating in the blood.^[3] There are higher concentrations of proinsulin after meals and lower levels when a person is fasting.^[3] Additionally, while proinsulin and insulin have structural differences, proinsulin does demonstrate some affinity for the insulin receptor. Due to the relative similarities in structure, proinsulin can produce between 5% and 10% of the metabolic activity similarly induced by insulin.^[3]

Proinsulin is the final single chain protein structure secreted by cells before cleavage into mature insulin.^[4] Proinsulin was discovered by Professor Donald F. Steiner of the University of Chicago in 1967.^[5]