What is insulin?

Insulin is a hormone secreted by islet β cells in human pancreas and contains 16 kinds of 5 1 amino acids. It is a small molecule protein with a molecular weight of 5 700, which is composed of two polypeptide chains A and B connected by two disulfide bonds. One chain has 2 1 amino acid residues, and there is also a disulfide bond in it, which connects the 6th and 1 1 amino acid residues. The B chain has 30 amino acid residues. Initially, insulin was extracted from animal pancreas.

Different kinds of animals (humans, pigs and cows, etc.). ) have different insulin components, but their functions are basically the same. The difference between human insulin and pig insulin is that the last amino acid residue of human insulin B chain is threonine, while pig is alanine. The difference between human insulin and bovine insulin lies in the A chain. The amino acid residues at position 8 and 10 in human are threonine and isoleucine, respectively, and alanine and valine in cattle. Different kinds of animals have different physiological functions and pharmacokinetics because of the differences in insulin structure.

In the process of human insulin synthesis, proinsulin containing 109 amino acids was formed, and its propeptide was quickly removed by protease hydrolysis in cells, forming a long peptide chain of 86 amino acids (84 in pigs)-proinsulin (molecular weight of human proinsulin is 9 000). Proinsulin forms β granules in Golgi complex. After the β-granule matures, the inactive C-peptide (human C-peptide is 365,438+0, pig is 29, and cow is 26) is removed from proinsulin by proteolytic enzyme, and the A-chain and B-chain at both ends form insulin and the remaining intermediate product (split proinsulin), which is secreted out of β cells and enters the blood circulation.