QUERCETIN, A POTENT AND SPECIFIC INHIBITOR OF THE HUMAN P-FORM PHENOLSULFOTRANSFERASE

The natural product quercetin was a potent inhibitor of the human P-fo rm phenolsulfotransferase with an IC50 value of 0.10+/-0.03 mu M (mean +/-SEM; N = 5), which was three to four orders of magnitude more poten t than its inhibition of other human sulfotransferases. The inhibition was noncompetitive with a K-i value of 0.10 mu M. The potency and mec hanism of this inhibition appear similar to those of the current stand ard P-form inhibitor, 2,6-dichloro-4-nitrophenol. Among other flavonoi ds examined, kaempferol was found to have an IC50 value of 0.39 +/- 0. 07 mu M, naringenin 10.6 +/- 1.6 mu M and naringin 265 +/- 90 mu M (N = 3). These observations suggest the potential for clinically importan t pharmacologic and toxicologic interactions by flavonoid-containing f oods and beverages.