Isolation of a new lipolytic-melanotropic peptide from human pituitary glands.

A new peptide having both lipolytic and melanotropic properties has been isolated from human pituitary glands. It has a molecular weight around 11,000, an amino acid composition different from the known lipolytic-melanotropic hormones, and an isoelectric point of 8.5. Although it is not entirely pure, there is no doubt that it differs from other known lipolytic-melanotropic substances in its total lack of methionine and tryptophan and its unusually high content of lysine and histidine. It has a melanocyte-stimulating hormone activity of 19 units/mug. As a lipolytic agent it is active with rabbit adipocytes, only slightly active with human cells and inactive with adipocytes from the rat.