Heterodimer of a B chain and an A chain; disulfide-linked (doubly). Secretory granules. Expressed in the cerebral light-green cells which are giant neuroendocrines cells involved in the control of growth. Belongs to the insulin family. PubMed:1572366 reported the formation of pyroglutamic acid by the N-terminal glutamic acid and of gamma-ethyl glutamate in peptide A. This is most probably an artifact of isolation.