Pituitary adrenocorticotrophin and the melanocyte stimulating hormones

Abstract

There are several structurally related peptides in the pituitary glands of vertebrates which possess a common heptapeptide sequence, namely Met-Glu-His-Phe-Arg-Trp-Gly. They comprise adrenocorticotrophin (ACTH), alpha-(melanocyte stimulating) hormone (α-MSH), beta-(melanocyte stimulating) hormone (β-MSH), beta-lipotrophin (β-LPH) and gamma-lipotrophin (γ-LPH). A sixth peptide, corticotrophin-like intermediate lobe peptide (CLIP), has recently been found in the pars intermedia of some animals and is identical with part of the C-terminal sequence of ACTH. These peptides are single-chained, devoid of cysteine residues (and consequently disulphide bridges) and, with the exception of α-MSH, have free amino and carboxyl groups on their terminal amino acids. The common heptapeptide sequence is found in the ACTH molecule at positions 4–10. Its position in the other peptides is shown in figure 13.1, from which it can be seen that, on the basis of sequence homology, these peptides fall naturally into two groups, one comprising ACTH, α-MSH and CLIP, and the other β-LPH, γ-LPH and β-MSH.