Opiomelanocortin family

Anterior pituitary hormones are classihed into three families the somatomammotropin family (GH and PRL), the glycoprotein hormones (LH, FSH, and TSH), and the opiomelanocortin family (ACTH, /i-endorphin, and related peptides). These three families appear to have evolved from three separate ancestral polypeptides homologous members of each family occur in other parts of the body. For example, human placental lactogen (hPL) is somatomammotropic, human chorionic gonadotrophin (hCG) is a glycoprotein hormone, and the brain and gut produce substances related to endorphins (enkephalins and dynorphin). 

Crowe RR, Noyes R Jr, Persico AM (1987a) Pro-opiomelanocortin (POMC) gene excluded as a cause of panic disorder in a large family. J Affect Disord 12 23-27 Crowe RR, Noyes R Jr, Wilson AF, Elston RC, Ward LJ (1987b) A linkage study of panic disorder. Arch Gen Psychiatry 44 933-937... 

One of the highly characterized prohormones is the pro-opiomelanocortin (POMC) also known as proadrenocorticotropin and 31 K ACTH/endorphin. The POMC family consists of peptides which act as hormones (ACTH, LPH, MSH) and others which may serve as neurotransmitters or neuromodulators (endorphins). POMC is synthesized as a precursor molecule of about 285 amino acids and is processed differently in various regions of the pituitary. One gene is responsible for POMC expression. 

Three separate categories of endogenous substances with morphine-like activity have been identified. These families of neuropeptides are known as enkephalins, endorphins, and dynorphins. Each family is derived from a distinct precursor polypeptide (pro-enkephalin, pro-opiomelanocortin, and prodynorfin) and has a characteristic anatomical distribution. The enkephalins and dynorphins found co-exist with other neurotransmitters, such as serotonin (5-HT) and noradrenaline, but details of how the peptides modulate the activity of co-transmitters await elucidation. 

Opium, derived from poppies, relieves pain and induces euphoria by binding to "opiate receptors" in the brain. These opioid drugs mimic the actions of three peptide families in the brain known as the endorphins, the enkephalins, and the dynorphins. These peptides, along with several nonopioid peptides (MSH, ACTH, lipotropin) are cleaved from the protein precursors pro-opiomelanocortin (POMC), proenkephalin, and prodynorphin (Fig. 3.5). 

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