Melanin Concentrating Hormone (MCH): Structure-Function Aspects of Its Melanocyte Stimulating Hormone-Like (MSH-Like) Activity

hormone (MCH): Structure-function aspects of its melanocyte stimulating hormone-like (MSH-like) activity. PEPTIDES 10(4) 773-778, 1989.--Melanin concentrating hormone (MCH) is a heptadecapeptide, Asp-Thr-Met-Arg-C~s-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-C)/s-Trp-Glu-Val, synthesized in the brain and secreted from the pars nervosa of teleost fish. This hormone stimulates melanosome (melanin granule) aggregation within integumental melanocytes of fishes but, in contrast, stimulates melansome dispersion within tetrapod (frog and lizard) melanocytes. We determined the message sequence ofthe primary structure of MCH which is responsible for its MSH-like component ofactivity. Removal of the N-terminal mino acid results in an almost otal oss of MSH-like activity. The C-terminal amino acid is also essential for full MSH-like activity since the analogue, MCH(I-16), is about 100 times less active than MCH. Therefore, the entire heptadecapeptide sequence of MCH appears to contribute to the MSH-like activity of MCH. Ring-contracted analogues (e.g., [AlaS,Cyst°]MCH) of MCH are almost devoid of any melanosome aggregating (MCH-like) activity but generally possess considerable oras great an MSH-like activity as MCH. Racemization fMCH by heat-alkali treatment drastically reduces the MCH-like activity of MCH, but does not enhance the MSH-like activity of the hormone. Melanin concentrating hormone (MCH) Melanocyte stimulating hormone-like activity Structure-function aspects MANY species of frogs, lizards, and fish are dependent upon hormonally-induced chromatic responses for their existence an