Partial N-terminal amino acid sequence of pro-opio-melanocortin (ACTH/beta-LPH precursor) from rat pars intermedia

Posterior lobes of rat pituitary (pars intermedia plus pars nervosa) were incubated with various labeled amino acids and the cell extracts analyzed by NaDodSO₄ polyacrylamide disc gel electrophoresis. Two forms of precursor proteins for betaendorphin and alpha-MSH were synthesized. Both forms have been shown to contain the fragments beta-LPH 61–69 and ACTH 1–8 and are thought to have the same peptide backbone. The two forms were simultaneously submitted to automatic Edman degradation and the following partial sequence was obtained: Trp/Arg₁-Leu₃-Phe₄-Ser₅-Ser₆-Leu₁₁-Thr_12–13-Tyr₁₄-Ser₁₅-Leu_17–18-Ala₁₉-lle₂₁-Arg_22–25- Leu_26–28-Ser₂₉. This sequence was compared with that reported by Nakanishi et al. (18). Their amino acids sequence was indirectly derived from DNA sequencing after isolation of mRNA from bovine pars intermedia. This comparison indicates the presence of a signal peptide of 26 amino acids in the sequence of beef ACTH/beta-LPH precursor.