Proenkephalin: Proteins and Enzymes

Enkephalins are small peptides derived from large precursers (pro-enkephalin A and B) containing multiple enkephalin copies. They are the most abundant opioid peptides in the body and are widely distributed in the brain and the peripheral nervous system and occur also in the adrenal medulla. Several types of neuroendocrine tumors, including pheochromocytomas, neuroblastomas and bronchial and gastrointestinal endocrine tumors, produce enkephalin.