In mammals including humans, insulin pro-hormone (like pro-enzyme, pro-hormone needs to be processed before becoming a fully mature and functional hormone) is synthesized; which has an additional extension called peptide 'C'. This peptide ‘C’ is not present in mature insulin, which is separated from insulin during maturation. Therefore, sugar level is controlled by giving processed pre-insulin to diabetic patients. Unprocessed pre-insulin cannot control the sugar level.