Proopiomelanocortin

Pro-opiomelanocortin (POMC) is a precursor polypeptide with 241 amino acid residues.

Production
It is synthesised by
 * corticotrope cells of the anterior pituitary gland
 * melanotrope cells of the intermediate lobe of the pituitary gland
 * about 3000 neurons in the arcuate nucleus of the hypothalamus
 * smaller populations of neurons in the dorsomedial hypothalamus and brainstem
 * melanocytes in the skin

Derivatives
The large molecule of POMC is the source of several important biologically active substances. POMC can be cleaved enzymatically into the following peptides:
 * adrenocorticotropic hormone (ACTH) and &beta;-LPH in the anterior pituitary gland
 * CLIP, &gamma;-LPH, &alpha;-MSH and &beta;-endorphin in the intermediate lobe
 * &gamma;-MSH
 * &beta;-MSH

Although the N-terminal 5 amino acids of beta-endorphin are identical to the sequence of Met-enkephalin, it is not generally thought that beta-endorphin is converted into Met-enkephalin. Instead, Met-enkephalin is produced from its own precursor, proenkephalin.

The production of beta-MSH occurs in humans but not in mice or rats due to the absence of the enzymatic processing site in the rodent POMC.

Functions
Each of these peptides is packaged in large dense-core vesicles that are released from the cells by exocytosis in response to appropriate stimulation.
 * &alpha;-MSH produced by neurons in the arcuate nucleus has important roles in the regulation of appetite and sexual behavior, while &alpha;-MSH secreted from the intermediate lobe of the pituitary regulates the production of melanin.
 * ACTH is a peptide hormone that regulates the secretion of glucocorticoids from the adrenal cortex.
 * &beta;-endorphin and met-enkephalin are endogenous opioid peptides with widespread actions in the brain.