RT Journal Article SR Electronic T1 Enzymology of Methylation of Tea Catechins and Inhibition of Catechol-O-methyltransferase by (−)-Epigallocatechin Gallate JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 572 OP 579 DO 10.1124/dmd.31.5.572 VO 31 IS 5 A1 Hong Lu A1 Xiaofeng Meng A1 Chung S. Yang YR 2003 UL http://dmd.aspetjournals.org/content/31/5/572.abstract AB (−)-Epigallocatechin gallate (EGCG) and (−)-epigallocatechin (EGC) are the major polyphenolic constituents in green tea. In this study, we characterized the enzymology of cytosolic catechol-O-methyltransferase (COMT)-catalyzed methylation of EGCG and EGC in humans, mice, and rats. At 1 μM, EGCG was readily methylated by liver cytosolic COMT to 4"-O-methyl-EGCG and then to 4′,4"-di-O-methyl-EGCG; EGC was methylated to 4′-O-methyl-EGC. The Km andVmax values for EGC methylation were higher than EGCG; for example, with human liver cytosol, theKm were 4.0 versus 0.16 μM andVmax were 1.28 versus 0.16 nmol/mg/min. Rat liver cytosol had higher COMT activity than that of humans or mice. The small intestine had lower specific activity than the liver in the methylation of EGCG and EGC. Glucuronidation on the B-ring or thed-ring of EGCG greatly inhibited the methylation on the same ring, but glucuronidation on the A-ring of EGCG or EGC did not affect their methylation. Using EGC and 3,4-dihydroxy-l-phenylalanine as substrates, EGCG, 4"-O-methyl-EGCG, and 4′,4"-di-O-methyl-EGCG were all potent inhibitors (IC50 ∼0.2 μM) of COMT. The COMT-inhibiting activity of (−)-EGCG-3′-O-glucuronide was similar to EGCG, but (−)-EGCG-4"-O-glucuronide was less potent. The present work provides basic information on the methylation of EGCG and suggests that EGCG may inhibit COMT-catalyzed methylation of endogenous and exogenous compounds. The American Society for Pharmacology and Experimental Therapeutics