- association (involving non-covalent bonds) of more than one polypeptide chain subunits to form a functional protein
The two-chain structure of insulin is not usually seen as the quaternary level since it is stabilised by disulphide bonds (and both chains came from a single polypeptide originally).
However, in the presence of mineral ions, insulin may associate to form dimers, tetramers etc. Zinc ions cause insulin to form into a stable hexamer (6 A & B chains). This hexameric form is found in beta-cells of the islets of Langerhans, and it is seen as helpful in prolonging the usefulness of insulin in treating diabetes. Show hexameric form ... show zinc
This graphics display was prepared to support a unit on the levels of protein structure using insulin as an example.