The basal arrangement appropriate for biological action of alpha-MSH (alpha-melanotropin, alpha-melanocyte aesthetic hormone) was bent in the frog (Rana pipiens) derma bioassay. The arrangement appropriate to arm-twist assessable biological action was the axial tetrapeptide sequence, Ac-His-Phe-Arg-Trp-NH2 (Ac-alpha-MSH6-9-NH2), which was about 6 orders of consequence beneath almighty than the built-in tridecapeptide.
Smaller bits of this arrangement (Ac-His-Phe-NH2, Ac-Phe-Arg-NH2, Ac-His-Phe-Arg-NH2) were bare of Melanotropi action at concentrations as top as 10(-4) M. We were clumsy to authenticate biological action 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 able a alternation of fragment analogues of alpha-MSH in an attack to actuate the accession of anniversary alone amino acerbic to the biological action of the built-in hormone. The basal authority of Ac-alpha-MSH6-9-NH2 could be added about a agency of 16 by the accession of glycine to the C-terminus, acquiescent Ac-alpha-MSH6-10-NH2 (Ac-His-Phe-Arg-Trp-Gly-NH2).
Addition of glutamic acerbic to the N-terminus provided the peptide, Ac-alpha-MSH5-10-NH2, which was alone hardly added almighty than Ac-alpha-MSH6-10-NH2, advertence that position 5 contributes little to the biological authority of alpha-MSH in this assay. Accession of methionine to the N-terminus of Ac-alpha-MSH5-10-NH2 resulted in the heptapeptide, Ac-alpha-MSH4-10-NH2, which was alone about 4-fold added almighty than Ac-alpha-MSH5-10-NH2.
