Hydrolysis of [Leu]enkephalin by chick brain in vitro

Using high-performance liquid chromatography with electrochemical detection to measure substrate disappearance and metabolite accumulation following addition of [Leu]enkephalin to samples prepared from chick brain in vitro, the following were found: 1. [Leu]enkephalin hydrolysis by whole forebrain homogenates is almost solely attributable to aminopeptidase MII activity. 2. [Leu]enkephalin hydrolysis by whole forebrain P2 membrane fractions is attributable to both aminopeptidase MII and dipeptidyl carboxypeptidase activity. 3. Differences are apparent in both [Leu]enkephalin disappearance and Tyr-Gly-Gly accumulation in P2 membrane fractions, but not in homogenate fractions, prepared from several regions of the chick brain.