title: alpha-Melanotropin: the minimal active sequence in the frog skin bioassay.
abstract: The minimal sequence required for biological activity of alpha-MSH (alpha-melanotropin, alpha-melanocyte stimulating hormone) was determined in the frog (Rana pipiens) skin bioassay. The sequence required to elicit measurable biological activity was the central tetrapeptide sequence, Ac-His-Phe-Arg-Trp-NH2 (Ac-alpha-MSH6-9-NH2), which was about 6 orders of magnitude less potent than the native tridecapeptide. Smaller fragments of this sequence (Ac-His-Phe-NH2, Ac-Phe-Arg-NH2, Ac-His-Phe-Arg-NH2) were devoid of melanotropic activity at concentrations as high as 10(-4) M. We were unable to demonstrate biological activity for the tetrapeptide, Ac-Phe-Arg-Trp-Gly-NH2 (Ac-alpha-MSH7-10-NH2), and for several carboxy terminal analogues including Ac-Lys-Pro-Val-NH2 (Ac-alpha-MSH11-13-NH2). We prepared a series of fragment analogues of alpha-MSH in an attempt to determine the contribution of each individual amino acid to the biological activity of the native hormone. The minimal potency of Ac-alpha-MSH6-9-NH2 could be enhanced about a factor of 16 by the addition of glycine to the C-terminus, yielding Ac-alpha-MSH6-10-NH2 (Ac-His-Phe-Arg-Trp-Gly-NH2). Addition of glutamic acid to the N-terminus provided the peptide, Ac-alpha-MSH5-10-NH2, which was only slightly more potent than Ac-alpha-MSH6-10-NH2, indicating that position 5 contributes little to the biological potency of alpha-MSH in this assay. Addition of methionine to the N-terminus of Ac-alpha-MSH5-10-NH2 resulted in the heptapeptide, Ac-alpha-MSH4-10-NH2, which was only about 4-fold more potent than Ac-alpha-MSH5-10-NH2. Addition of lysine and proline to the C-terminal of the Ac-alpha-MSH4-10-NH2 sequence yielded the peptide, Ac-alpha-MSH4-12-NH2 with a 360-fold increase in potency relative to Ac-alpha-MSH4-10-NH2. This peptide was only about 6-fold less potent than alpha-MSH. A series of Nle-4-substituted analogues also were prepared. Ac-[Nle4]-alpha-MSH4-10-NH2 was about 4 times more potent than Ac-alpha-MSH4-10-NH2. Ac-[Nle4]-alpha-MSH4-11-NH2 also was about 4 times more potent than Ac-alpha-MSH4-10-NH2, demonstrating that lysine-11 contributes somewhat to the biological activity of alpha-MSH on the frog skin melanocyte receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry, University of Arizona 85721.
authors.forename: V J
authors.initials: VJ
authors.lastname: Hruby
authors.forename: B C
authors.initials: BC
authors.lastname: Wilkes
authors.forename: M E
authors.initials: ME
authors.lastname: Hadley
authors.forename: F
authors.initials: F
authors.lastname: Al-Obeidi
authors.forename: T K
authors.initials: TK
authors.lastname: Sawyer
authors.forename: D J
authors.initials: DJ
authors.lastname: Staples
authors.forename: A E
authors.initials: AE
authors.lastname: de Vaux
authors.forename: O
authors.initials: O
authors.lastname: Dym
authors.forename: A M
authors.initials: AM
authors.lastname: Castrucci
authors.forename: M F
authors.initials: MF
authors.lastname: Hintz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001681:Biological Assay; D066298:In Vitro Techniques; D010446:Peptide Fragments / Q000494:pharmacology*; D011894:Rana pipiens; D012867:Skin / Q000187:drug effects; D013329:Structure-Activity Relationship; D000521:alpha-MSH / Q000494:pharmacology*
chemical_list: D010446:Peptide Fragments; D000521:alpha-MSH