Relatively a small protein, with a molecular weight of about 6000 Daltons.

The insulin mRNA is translated as a single chain precursor called preproinsulin, and removal of its signal peptide during insertion into the endoplasmic reticulum generates proinsulin.

Within the endoplasmic reticulum, proinsulin is exposed to several specific endopeptidases which excise the C peptide, thereby generating the mature form of insulin.

Insulin and free C peptide are packaged in the Golgi into secretory granules which accumulate in the cytoplasm. When the B cell is appropriately stimulated, insulin is secreted from the cell by exocytosis and diffuses into islet capillary blood.

Secreted primarily in response to elevated blood concentrations of glucose.

Neural stimuli (e.g. site and taste of food) and increased blood concentrations of other fuel molecules, including amino acids and fatty acids, also promote insulin secretion.

It is thought that elaevated glucose levels within the B cell leads to membrane depolarization and an influx of extracellular calcium. The resulting increase in intracellular calcium is thought to be one of the primary triggers for exocytosis of insulin-containing secretory granules.