Proinsulin (PI), a polypeptide of 9390 MW (86 amino acids) is synthetized in the β cells of the Islets of Langerhans in the pancreas. The sequence of proinsulin is highly conserved in mammalian species and is homologous with IGF-1 and IGF-2. This protein is processed to C-peptide and insulin forms. Both are secreted in equimolar amounts into the blood. In normal individuals, proinsulin is present in the circulatioon in very low concentrations (typical basal values 2–6 pmol/l). The level of proinsulin in serum can be a reflection of β cell status and a consequence of disfunction of PI processing and/or secretion. Proinsulin like material is increased in clinical conditions as insulinoma, familial hyperinsulinemia, non-insulin dependent diabetes mellitus. Clinical applications: Proinsulin is the precursor of insulin, which is the principal hormone responsible for the control of glucose metabolism. The measurement of Proinsulin in serum provides useful valuable information for the diagnosis of insulinomas. Proinsulin levels have also been shown to be elevated in non-insulin dependent diabetics (NIDDM), in insulin dependent diabetics (IDDM) and other clinical situations.
- References to Proinsulin