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 Ki) 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.