抄録
In vivo MSH activities of three decapeptides, Gly1-ACTH (1-10) OH, Ibu1-ACTH (1-10) OH, β-Ala1-ACTH (1-10) OH, and a tetradecapeptide Gly1-ACTH (1-14) OH were compared with those of three octadecapeptides having N-terminal amino acid residues common to the respective shorter peptides; Gly1-ACTH (1-18) NH2, ACTH (1-18) NH2, and β-Ala1-ACTH-(1-18) NH2. The three decapeptides had almost the same minimum effective dose in assays in African frog, Xenopus laevis D. The potencies of three decapeptides were about 1/1, 000 of the potency of α-MSH on a weight basis and the tetradecapeptide was 1/640. The octadecapeptides, however, showed differing MSH potencies: Glyi-ACTH (1-18) NI12 was 1/48 as potent as α-MSH;β-Ala1-ACTH (1-18) NH2 and Ibu1-ACTH (1-18) NH2 exhibited 1/1.5-1/2.5 of the potency of α-MSH respectively. A possible mechanism explaining why the effect of substitution of the Nterminal residue on MSH activity is different in decapeptides and octadecapeptides is considered.
