Comparative biological activities of potent analogues of α‐melanotropin: Effect of nonaromatic and para substituted aromatic amino acids at position 7

BRIAN C. WILKES, WAYNE L. CODY, VICTOR J. HRUBY, ANA MARIE DE L. CASTRUCCI, MAC E. HADLEY

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Abstract

Several α‐melanotropin (α‐MSH) analogues with para substituted aromatic and nonaromatic amino acids in the 7‐position of the hormone were prepared and their melanotropic activities determined in the frog (Rana pipiens) and lizard (Anolis carolinensis) skin bioassays. D and L‐Phe(p‐NO2), D‐ and L‐Tyr, D‐ and L‐Ala, and Gly were substituted in the 7‐position. The use of substituted D or L‐aromatic amino acids in the 7th position of the central Ac‐[Nle4] ‐α‐MSH4–11 ‐ NH2 fragment resulted in a loss in potency relative to the corresponding phenylalanine‐containing analogue. The loss in potency cannot be due entirely to steric hindrance at the melanophore receptor, since nonaromatic amino acids substituted in the 7th position of this octapeptide fragment also generally led to a loss in biological activity. We reported previously that replacement of phenylalanine‐7 by its D enantiomer led to a marked increase in potency in each fragment analogue tested. Analogues containing other D amino acids in the 7th position also were more potent than their L amino acid‐containing analogues with one exception: Ac‐[Nle4, Ala7]‐α‐MSH4–11‐NH2 was more potent than Ac‐[Nle4, D‐Ala7]‐α‐MSH4–11‐NH2 in the frog skin bioassay. Replacement of phenylalanine‐7 by glycine resulted in a large decrease in potency in both bioassays, illustrating the importance of the side chain group, in this position of α‐MSH, to biological potency of the hormone.

Original languageEnglish (US)
Pages (from-to)685-694
Number of pages10
JournalInternational journal of peptide and protein research
Volume27
Issue number6
DOIs
StatePublished - Jun 1986

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Keywords

  • melanocytes
  • peptide diastereoisomers
  • position 7
  • structure‐activity relationships
  • α‐MSH

ASJC Scopus subject areas

  • Biochemistry

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