A 51-amino acid pancreatic hormone that plays a major role in the regulation of glucose metabolism, directly by suppressing endogenous glucose production (glycogenolysis; gluconeogenesis) and indirectly by suppressing glucagon secretion and lipolysis. Native insulin is a globular protein comprised of a zinc-coordinated hexamer. Each insulin monomer containing two chains, A (21 residues) and B (30 residues), linked by two disulfide bonds. insulin is used as a drug to control insulin-dependent diabetes mellitus (diabetes mellitus, type 1).