N-TERMINAL TETRAPEPTIDE OF DERMORPHIN AND D-ARG-SUBSTITUTED TETRAPEPTIDES - INACTIVATION PROCESS OF THE ANTINOCICEPTIVE ACTIVITY BY PEPTIDASE

Degradation products of the N-terminal tetrapeptide of dermorphin, HTyrDAlaPheGlyOH (ALPG) and D-Arg2-substituted tetrapeptide analogs of dermorphin, HTyrDArgPheGlyOH (ARPG), HTyrDArgPheGlyNH2 (TDAPGNH2) and HTyrDArgPheβAlaOH (TDAPA) by enkephalin degrading enzymes were studied by using reversed-phase high-performance liquid chromatography. After 5 and 25 hr incubations of the peptides with solubilized enzymes of mouse brain or spinal cord, liberation of the appreciable Tyr1 residue was observed in ALPG but not in ARPG, TDAPGNH2 and TDAPA. When ARPG and TDAPGNH2 were incubated with enzymes for 25 hr, a main degradation product was the N-terminal tripeptide produced from the hydrolysis of Phe3Gly4 bond. Conversely, TDAPA did not produce the N-terminal tripeptide after 25 hr incubation with enzymes. In the enzyme assay, Tyr1-D-Arg2 bond of ARPG, TDAPGNH2 and TDAPA was more stable than that of ALPG to the cleavage by aminopeptidase M (APM). Phe3Gly4 bond of ALPG, ARPG and TDAPGNH2 were easily hydrolyzed by carboxypeptidase Y (CPY) within 3 hr incubation, whereas the hydrolysis of Phe3βAla4 bond of TDAPA by CPY was not observed after 3 hr incubation. The present results and previous behavioural data suggest that a potent and prolonged antinociceptive activity of the D-Arg-substituted tetrapeptides is mainly attributed to the stability of Tyr1DArg2 bond against aminopeptidase of peptidases. © 1990.