Identification and characterization of two distinct kyotorphin-hydrolyzing enzymes in rat brain

We identified and characterized two kyotorphin-hydrolyzing peptidases (KTPases) in a soluble fraction of rat brain. When the soluble fraction was chromatographed with DEAE-Sephacel, the enzyme activity was resolved into two peaks, which were designated as KTPases I and II in their order of elution. KTPases I and II accounted for 95% and 5% of the KTPase activity in the soluble fraction, respectively. KTPases I and II hydrolyzed kyotorphin with Km values of 22 microM and 110 microM, respectively. By gel filtration, Mr values of KTPases I and II were determined to be 55,000 and 98,000, respectively. Immunological analyses of KTPase II with an anti-enkephalin aminopeptidase antibody indicated that KTPase II was identical to an enkephalin aminopeptidase with Mr = 98,000. However, KTPase I was a novel peptidase responsible for the major kyotorphin-degrading activity in the soluble fraction of rat brain.