Biosynthesis of a γ3‐Melanotropin‐like Peptide in the Pars Intermedia of the Amphibian Pituitary Gland

Abstract
The biosynthesis of a .gamma.3-melanotropin-like peptide in the pars intermedia of the pituitary gland of the aquatic toad Xenopus laevis is revealed. Pulse-chase experiments in vitro showed that this product is synthesized through processing of a prohormone, pro-opiomelanocortin, and that it is released into the incubation medium. The peptide immunoprecipitated with antiserum to .gamma.3-melanotropin, appeared to be a glycopeptide and displayed melanotropic activity. This last observation together with the results of tryptic and chymotryptic peptide mapping of the newly synthesized product indicates that Xenopus .gamma.3-melanotropin is structurally different from the proposed mammalian .gamma.-melanotropins.

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