After removal of the precursor signal peptide, proinsulin is post-translationally cleaved into three peptides: the B chain and A chain peptides, which are covalently linked via two disulfide bonds to form insulin, and C-peptide. Binding of insulin to the insulin receptor (INSR) stimulates glucose uptake.
Veedfald S, Plamboeck A, Deacon C F, et al. Cephalic phase secretion of insulin and other enteropancreatic hormones in humans[J]. American Journal of Physiology-Gastrointestinal and Liver Physiology, 2016, 310(1): G43-G51.