ABSTRACT
α-Melanotropin plays an essential role in the control of melanin pigmentation of the skin of many animals. The enzymology of MSH and related analogues may lead to the design of clinically useful melanotropins that exhibit resistance to inactivation by digestive or serum enzymes. Several studies using MSH in the presence of proteolytic enzymes have suggested that the hormone was resistant to exopeptidases, probably due to N-terminal acetylation and C- terminal amidation. Chemical messengers such as hormones, whatever their method of delivery to their target cells, must often be metabolized rather rapidly if a precise control is to be established. Immunocytochemical studies have shown that MSH and/or related peptides are localized in neurons within the mammalian brain, and MSH has been implicated in processes related to memory, learning, and attention in mammals, including humans. Peptide hormones have relatively short half-lives as would be expected if they are to provide a precise control of target tissues.
