Noncompetitive, reversible inhibition of aminoacylase-1 by a series of L-α-hydroxyl and L-α-fluoro fatty acids: Ligand specificity of Aspergillus oryzae and porcine kidney enzymes

L-Lactate and L-β-phenyllactate have been identified in the culture broth of Streptomyces sp. KY-11 as reversible noncompetitive inhibitors of Aspergillus oryzae aminoacylase-1 and porcine kidney Aminoacylase I. A series of α-hydroxyl acids (DL-R-CH(OH)COOH, R = Et, n-pro, n-butyl, n-pentyl, n-hexyl) also inhibited the two enzymes in reversible noncompetitive kinetics, and the inhibition potency (-log K(i)) increased with the increased hydrophobicity of the R group. The two eukaryotic enzymes showed distinct preferences to the ligand α-alkyl group, and the fungus enzyme was inhibited by L-β-phenyllactate (R = benzyl) 10³-fold more potently than the mammalian enzyme. L-α-Fluoro-β-phenyl-propionate and its D-isomer were used to show that the L-configuration of the α-substituent was important for potent inhibition of both the enzymes. The fungus aminoacylase-1 steeply decreased the affinity to α-fluoro- and α-hydroxy-n-caproate as pH was raised from 7 to 11, whereas the mammalian enzyme retained the affinity to these ligands under alkaline conditions. These results suggest that A. oryzae aminoacylase-1 has an acidic residue that interacts with -OH or -F, while the mammalian enzyme would have a basic residue that recognizes the α-substituents. (C) 2000 Academic Press.