Melanotropins activity

While these studies were in progress, a series of extensive studies on the minimum active sequences necessary for biological activity in melanotropin peptide at pigment cell receptor. Through use of a series of assays and animals it was determined that the His-Phe-Arg-Trp segment of a-MSH was the minimum sequence for full agonist activity (147,148). 

In addition, both ACTH and MSH stimulate lipolysis in rabbit adipose tissue. That the melanophore stimulating activity associated with purified ACTH is intrinsic to the hormone and not due to contamination with the melanotropins, was conclusively demonstrated by the synthesis of a nonadecapeptide corresponding to the first 19 residues of ACTH ( ). This synthetic peptide stimulated steroidogenesis in the adrenal gland and also elicited melanin dispersion. 

Sawyer, T. K., Hruby, V. J., Darman, P. S., and Hadley, M. E. (1982) [half-Cys4,half-Cys 10] -alpha-Melanocyte-stimulating hormone A cyclic alpha-melanotropin exhibiting superagonist biological activity. Proc. Natl. Acad. Sci. U.S.A. 79, 1751-1755. 

Eberle, A.N. (1988) Structure-activity relationships of the melanotropins. In The Melanotropins Chemistry, Physiology and Mechanism of Action, Karger, Basel, pp. 333-379. 

According to Pawelek et al. 200), the biosynthesis of melanin in Cloudman melanoma cells is a complex process and is regulated by three factors (a) a dopamine conversion factor which converts dopamine to 5,6-dihydroxyindole (13), (b) a 5,6-dihydroxyindole conversion factor which catalyzes the conversion of 5,6-dihydroxyindole to melanin and is active when cells are exposed to melanotropin (MSH), and (c) a 5,6-dihydroxyindole blocking factor which restricts melanogenesis at the 5,6-dihydroxyindole stage. They have also shown that at least three steps in the Raper-Mason scheme of melanin formation from tyrosine are catalysed by tyrosinase (Fig. 6). 

Corticotropin, adrenocorticotropln, adrenocorticotropic hormone, ACTH a polypeptide hormone secreted by the pituitary. The primary structure of the human hormone is Ser-T -Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-Gly-Lys-Lys-Arg-Arg-Pro-Val-Lys-Val-Tyr-Pro-Asn-Gly-Ala-Glu-Asp-Glu-Leu-Glu-Phe, M, 4541. Only sequence 31-33 is species-specific. Biological activity is determined by the first (hxed) 20 amino acids. Sequence 1-13 is identical to that of a-melanotropin. 

P. occur widely and have many different biological functions. Many are hormones, e.g. Corticotropin, Melanotropin, Oxytodn, Vasopressin, Releasing hormones, Insulin, Glucagon, Gastrin, Secretin, Angiotensin, Bradykinin, Endorphins, Opioid peptides (see entries for each of these). Many microorganisms produce P., often with antibiotic activity (see Peptide antibiotics). Some P. are very toxic, e.g. Phallotoxins (see), Amatoxins (see) and Melittin (see). Very simple P. are... 

These studies support our model of the putative conformation of a-MSH at the melanotropin receptor. However, it is clear that the 4-10 residues by themselves are insufficient for superagonist activity, but also require related interactions of the Lys-... 

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