The number of peptides in proinsulin remains constant at three regardless of the type of proinsulin. However, unlike insulin, proinsulin is a single polypeptide made up of these three peptides, and there are differences between them. The number of peptides in proinsulin and their characteristics is discussed in this article. The first peptide in proinsulin is known as chain A.
Peptide A
Peptide A or the “A-chain”, is the first peptide in proinsulin. It remains in the structure of the molecule until the proinsulin converts to insulin. The second peptide – peptide “B” – does the same. Peptide A and peptide B are connected by the C-chain, but the connection between peptide A and the connecting C-chain is much stronger than that between peptide B and the “C-chain”.
Peptide B
Peptide B is a chain of amino acids that is slightly shorter than that of peptide A. The connection between peptide B and the C-chain is weaker than that between peptide A and the C-chain; however, the connection between peptide B and the chain is recognized as one of the best conserved biochemical structures throughout evolution and is thought to be critical to the formation of insulin from proinsulin.
The C-Chain
The C-chain is the chain that connects peptide A and peptide B. However, when proinsulin converts to insulin, the C-chain is lost and becomes three di-sulphide bonds; two bonds between peptide A and peptide B and one within peptide A itself. The structure of the C-chain in proinsulin and its connections to peptide A and peptide B are critical to the formation of healthy mature insulin through the set up of these three di-sulphide bonds from the C-chain.
Summary
Proinsulin is a polypeptide chain made up of three peptides. These convert to a binary structure in insulin by the formation of disulphide bonds from the connecting C-chain.
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