Managing diabetes is possible by administering insulin periodically. Insulin used for diabetes was earlier extracted from pancreas of slaughtered cattle and pigs. However, this insulin caused some people to develop allergies and other types of reactions. In mammals, including humans, insulin is synthesized as a prohormone and is later converted to insulin.

Identify A and B in the picture.

A: Proinsulin

B: Chain C

In mammals, insulin is secreted as pro-hormone which contains an extra peptide C which is not present in  mature insulin .