Insulin is a hormone secreted by the beta cells of the islets of Langerhans in the pancreas. It promotes glycogen storage, formation of triglycerides, and synthesis of protein and nucleic acids.  It regulates carbohydrate, protein and lipid metabolism by enhancing membrane transport of glucose, amino acids, and certain ions. It also promotes glycogen storage, formation of triglycerides and synthesis of proteins and nucleic acids. Insulin is 51-amino acid polypeptide product produced from a precursor peptide, proinsulin. Proinsulin is post-translationally cleaved into two chains (peptide A and peptide B) that are covalently linked via two disulfide bonds and one molecule of C-peptide. Insulin deficiency results in diabetes mellitus, one of the leading causes of morbidity and mortality in the general population. Insulin is also present in tumors of b-cell origin such as insulinoma.

 

Reports of immunocytochemical investigation reveal the presence of insulin in the cytoplasm of certain islet tumors. However, in some instances insulin-positive granules are sparse and form a margin against the cell membrane.