Insulin is a hormone secreted by beta cells within the pancreas. It is essential in regulating the metabolism of carbohydrates and fats in the body.
The hormone insulin is a peptide hormone consisting of 2 polypeptide chains.
Primary structure (amino acid sequence) :
In the beta cells within islets of Langerhans of the pancreas, insulin is originally produced as a single molecule preproinsulin (composed of 110 amino acids).
After preproinsulin has passed through the endoplasmic reticulum, 24 amino acids (“the signal peptide”) are removed by enzyme action from one end of the chain, leaving another form Pro-insulin, which folds and bonds to give the molecule much of the final structure
It is composed of two peptide chains referred to as the A chain and B chain. A and B chains are linked together by two disulfide bonds, and an additional disulfide is formed within the A chain. In most species, the A chain consists of 21 amino acids and the B chain of 30 amino acids.
Image courtesy of Isaac Yonemoto at wikipedia.org