In situ characterization of nasal leucine enkephalin degrading aminopeptidase susceptibility of the nasal enzyme to boronic acids and phosphorus-containing peptide and amino acid isosteres

Abstract

The N-terminal Tyr-Gly bond of leucine-enkephalin is specifically hydrolyzed during exposure to the nasal mucosa. Kinetic properties in situ indicate that this activity is due to a single enzyme which has a KMapp of 0.4 mM for leucine-enkephalin. Analysis of initial rates of hydrolysis from earlier inhibition studies using boroalanine, boroleucine, and borovaline indicated that these inhibitors bind the nasal enzyme with Kmapp values of 0.009-0.02 μM. In addition, we have evaluated borophenylalanine (Kappi = 0.004 μM) in this study. Similarly, H-PheΨP(O)(OH)CH2Phe-OMe binds the nasal aminopeptidase with a Kappi of 0.2 μM. Comparison of these Ki values with those of cytosolic aminopeptidase and microsomal aminopeptidase derived from porcine kidney, indicates that the nasal enzyme closely resembles the microsomal enzyme in properties. Major distinctions between the enzymes are: (1) the greater dependence of the cytosolic enzyme on the nature of the amino acid residue in the primary site (2) a much greater preference of both the microsomal and nasal enzyme for HPheΨ[P(O)(OH)CH2]Phe-OMe over H-PheΨ[P(O)(OH)2]. © 1995.