Table 2.

Initial rates of reduction for cytochrome c by xanthine oxidase + xanthine in the presence of natural product. Also shown are rates following 10 minute incubations of enzyme with 25 μM natural products and cytochrome c prior to the addition of xanthine. Final reaction mixtures were monitored over several minutes at 550 nm and contained 50 nM XO, 100 μM xanthine, natural product, and 75 μM cytochrome c. Error expressed as standard deviations from triplicate trials.

		Rate of cyt c reduction (nM · s−1)
Luteolin
	Control	160 ± 0.6
	10 μM	100 ± 3
	25 μM	82 ± 9
	50 μM	71 ± 3
	Incubation	110 ± 10
	(Control)	(170 ± 20)
Quercetin
	Control	170 ± 1
	10 μM	140 ± 20
	25 μM	100 ± 7
	50 μM	80 ± 6
	Incubation	110 ± 7
	(Control)	(170 ± 20)
Curcumin
	Control	160 ± 20
	10 μM	160 ± 7
	25 μM	150 ± 6
	50 μM	150 ± 6
	Incubation	150 ± 10
	(Control)	(170 ± 20)
Silibinin
	Control	160 ± 0.6
	10 μM	160 ± 7
	25 μM	150 ± 17
	50 μM	140 ± 13
	Incubation	120 ± 4
	(Control)	(170 ± 20)
Allopurinol
	Control	170 ± 10
	10 μM	140 ± 10
	25 μM	140 ± 6
	50 μM	120 ± 9
	Incubation	28 ± 1
	(Control)	(170 ± 20)