Estimation of Relative Importance of Three Enzymes in the Inactivation of [Met⁵]-Enkephalin and [Met⁵]-Enkephalin-Arg⁶ in Three Isolated Preparations by Employing the Inhibitor Specific for Each Enzyme

Abstract

The relative importance of three enzymes, amastatin-sensitive aminopeptidase, captopril-sensitive peptidyl dipeptidase A and phosphoramidon-sensitive endopeptidase-24.11, to inactivate two opioid peptides, [Met⁵]-enkephalin and [Met⁵]-enkephalin-Arg⁶, was investigated in three in vitro isolated preparations, guinea-pig ileum, mouse vas deferens and rat vas deferens, by estimating the magnitude of the enhancement of the inhibitory potency of the opioid peptide by each peptidase inhibitor. Results showed that the relative importance of the three enzymes in the inactivation of the opioid peptide, whether it was [Met⁵]-enkephalin or [Met⁵]-enkephalin-Arg⁶, in guinea-pig ileum was significantly different from that in either mouse vas deferens or rat vas deferens. Additionally, the relative importance of the three enzymes in the preparation, whether it was guinea-pig ileum, mouse vas deferens or rat vas deferens, in the inactivation of [Met⁵]-enkephalin was significantly different from that of [Met⁵]-enkephalin-Arg⁶. The significance of the presence of plural inactivating-enzymes for opioid peptides was discussed.