EFFECTS OF FLAVONOID COMPOUNDS ON THE ACTIVITY OF NADPH DIAPHORASE PREPARED FROM THE MOUSE-BRAIN

The effects of flavonoids on NADPH diaphorase activity were studied in vitro, and we found that the enzyme activity was markedly inhibited by quercetin. This inhibitory action was shown to be accompanied by an increase in the apparent K-m value of the enzyme for the cofactor NADPH, with a decrease in the V-max, and an increase in the apparent K-m for the substrate nitro blue tetrazolium, without any significant change in the V-max. These results indicate that quercetin may directly inhibit NADPH diaphorase, thus suggesting the possibility that this compound may be able to inhibit the production of nitric oxide in the brain.