Adrenocorticotropin. 49.1 Synthesis and biological activity of [2-delta-aminovaleric acid, 5-arginine-a1adrenocorticotropin-(2-19)

An adrenocorticotropin analogue, [2-delta-aminovaleric acid, 5-arginine]adrenocorticotropin-(2-19), has been synthesized by the solid-phase method and its biological activity has been determined. It was found that substitution of arginine for glutamic acid at position 5 of [2-delta-aminovaleric acid]adrenocorticotropin-(2-19) increased the steroidogenic potency in idolated rat adrenal cells and the lipolytic potency in isolated rat fat cells but decreased the lipolytic potency in isolated rabbit fat cells. The synthetic analogue had only 2% of the melanotropic potency of the parent molecule.

[Spectral studies of beta-melanocyte-stimulating hormone and beta-lipotropic hormone fragment]

Secondary structure of beta-melanocyte-stimulating hormone was studied by circular dichoism and infra-red spectroscopy. Left-helical conformation of poly-L-proline II type which was stabilized by temperature reduction was found in aqueous solution; in 60% ethanole the quota of this structure sharply decreased. The investigation of hormone films at different values of relative humidity (in the course of H--D metabolism) made it possible to discover a twisted beta-form and an elongated helix of poly-L-proline II type. Temperature induced changes of circular dichroism spectra specify the peculiarities of poly-L-proline II conformation in C-end fragment of beta-lipotropic hormone.

Tertiary structure of H-Pro-Leu-Gly-NH2, the factor that inhibits release of melanocyte stimulating hormone, derived by conformational energy calculations

Conformational energy calculations were carried out on H-Pro-Leu-Gly-NH(2), the factor that inhibits the release of melanocyte stimulating hormone, and its biologically active analog, H-Pro-Ala-Gly-NH(2). Both peptides were found to be relatively compact molecules that retain, however, some degree of flexibility. After structure refinement, H-Pro-Leu-Gly-NH(2) possesses at least three preferred compact conformations. Two of these conformations occupy rather broad and flat energy troughs, while a third occupies a narrow and deep potential energy well. This third structure, which consists of a 10-membered beta-turn closed by a (4 --> 1) hydrogen bond between the proton of the trans carboxamide of Gly and the C=O of Pro, is the one that was proposed for H-Pro-Leu-Gly-NH(2) in dimethylsulfoxide and was also found by x-ray analysis.