Mention the chemical change that proinsulin undergoes to be able to act as mature insulin.

Figure 1: Conversion of proinsulin to insulin
Proinsulin is the precursor of insulin which is stored in the beta islet cells of Langerhans in the pancreas. Proinsulin is a single polypeptide chain composed of the B and A subunits of insulin joined by the C-peptide region.The chemical change that proinsulin undergoes is cleavage of the C peptide with the aid of two endoproteases i.e. type I and type II endoproteases. This change takes place in islet cells of Langerhans, while proinsulin is transported through the Golgi apparatus for cleavage (See figure 1)