mention the chemical change that proinsulin undergo to be able to act as mature insulin
post translational modification
title: Proinsulin text: 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. Proinsulin is the final single chain protein structure secreted by cells before cleavage into mature insulin. Proinsulin was discovered by Professor Donald F. Steiner of the University of Chicago in 1967. Proinsulin is made up of 81 residues and formed by three distinct chains. The A chain, B chain, and the area connecting the two named the C peptide. The correct structure of proinsulin is crucial for the correct folding of mature insulin, as the title: Proinsulin text: form mature insulin. Mature insulin has 35 fewer amino acids; 4 are removed altogether, and the remaining 31 form the C-peptide. The C-peptide is abstracted from the center of the proinsulin sequence; the two other ends (the B chain and A chain) remain connected by disulfide bonds. The post translational modification of proinsulin to mature insulin only occurs in the beta cells of the islets of Langerhans. When proinsulin is transported through the Golgi apparatus the C-peptide is cleaved. This cleavage occurs with the aid of two endoproteases. Type I endoproteases, PC1 and PC3, disrupt the C peptide-B chain connection. title: Insulin text: beta cells. Preproinsulin contains a 24-residue signal peptide which directs the nascent polypeptide chain to the rough endoplasmic reticulum (RER). The signal peptide is cleaved as the polypeptide is translocated into lumen of the RER, forming proinsulin. In the RER the proinsulin folds into the correct conformation and 3 disulfide bonds are formed. About 5–10 min after its assembly in the endoplasmic reticulum, proinsulin is transported to the trans-Golgi network (TGN) where immature granules are formed. Transport to the TGN may take about 30 min. Proinsulin undergoes maturation into active insulin through the action of cellular endopeptidases known as prohormone title: Proinsulin text: PC2, a type II endoprotease, cleaves the C peptide-A chain bond. The resulting molecule, now mature insulin, is stored as a hexamer in secretory vesicles and is stabilized with formula_1 molecules until it is secreted. When insulin was originally purified from bovine or porcine pancreata, all the proinsulin was not fully removed. When some people used these insulins, the proinsulin may have caused the body to react with a rash, to resist the insulin, or even to make dents or lumps in the skin at the place where the insulin was injected. This can be described as an iatrogenic injury title: Proinsulin text: ability to properly fold the protein. This stress, after a while, would lead to a decrease in the number of β-cells producing mature insulin, and would then lead to diabetes mellitus. Postnatal proinsulin is crucial for metabolic regulation. However, proinsulin in neonates is important for normal development of the nerves of the eye, development of the heart, and general survival of embryonic cells. Regulation of the concentration of proinsulin during embryonic development is crucial, as too much or too little of the peptide can cause defects and death of the fetus. Thus far in the study of neonatal diabetes mellitus,