Antioxidative galloyl esters as enzyme inhibitors of p-hydroxybenzoate hydroxylase

Gallic acid and its esters were evaluated as enzyme inhibitors of recombina nt p-hydroxybenzoate hydroxylase (PHBH), a NADPH-dependent flavin monooxyge nase from Pseudomonas aeruginosa, n-Dodecyl gallate (DG) (IC50=16 muM) and (-)-epigallocatechin-3-O-gallate (EGCG) (IC50 = 16 muM), a major component of green tea polyphenols, showed the most potent inhibition, while product- like gallic acid did not inhibit the enzyme significantly (IC50 > 250 muM)- Inhibition kinetics revealed that both DG and EGCG inhibited PHBH in a non -competitive manner (K-I = 18.1 and 14.0 muM, respectively). The enzyme inh ibition was caused by specific binding of the antioxidative gallate to the enzyme, and by scavenging reactive oxygen species required for the monooxyg enase reaction. Molecular modeling predicted that EGCG binds to the enzyme in the proximity of the FAD binding site via formation of three hydrogen bo nds. (C) 2000 Federation of European Biochemical Societies, Published by El sevier Science B.V. All rights reserved.