A proenkephalin A-derived peptide analogous to bovine adrenal peptide E from frog brain: Purification, synthesis, and behavioral effects

A peptide derived from the posttranslational processing of proenkephalin A was isolated from an extract of the brain of the European green frog Rana ridibunda and its primary structure established as: Tyr-Gly-Gly-Phe-Met-Arg-Arg-Val-Gly-Arg¹⁰ Pro-Glu-Trp-Trp-Gln-Asp-Tyr-Gln-Lys-Arg²⁰-Tyr-Gly-Gly-Phe-Met. The structure was confirmed by chemical synthesis. The peptide represents an amphibian equivalent of bovine adrenal peptide E [preproenkephalin A(206-230)peptide] but the sequence contains two amino acid substitutions (Met¹⁵→Gln and Leu²⁵→Met) compared with the mammalian peptide. The data support previous hypotheses that the Leu-enkephalin sequence is not present in preproenkephalin A of amphibians. Intracerebroventricular injections of frog peptide E ( 10 and 100 ng) in mice had no significant effect on horizontal locomotor activity. The peptide, in doses up to 1 pg, had no effect on latency of escape jumping in the hot plate test and the peptide (100 ng) did not modify responses (paw licking, rearing, and escape jumping) in morphine-treated mice.