Racemization of alpha-melanotropin.
Racemization of the amino acid residues of alpha-melanotropin was measured after exposure of the peptide to alkali for various lengths of time. Rates of racemization were then compared to the rate of transformation by alkali of alpha-melanotropin into a hormone with prolonged melanotropic activity. When in vitro prolongation became maximal, serine, methionine, histidine, phenylalanine and arginine were racemized 50-70%, glutamic acid, tyrosine and tryptophan 30-40% and lysine, proline and valine 10% or less. Racemization of a particular amino acid residue in alpha-melanotropin could not be associated with induction of prolongation of activity. Rather, partial racemization at multiple sites in the molecule seems almost as effective as extensive or total racemization of a single residue in producing a hormone with prolonged biological effects.
Lande
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Department of Dermatology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Conn. 06510, USA.
Lerner
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D000596:Amino Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D021122:Protein Subunits; D013237:Stereoisomerism; D000521:alpha-MSH / Q000737:chemistry*; D019824:beta-MSH / Q000737:chemistry
D000596:Amino Acids; D021122:Protein Subunits; D019824:beta-MSH; D000521:alpha-MSH