Rate of glucuronidation of regiospecific glucuronides of Fnol (a), 4’HFnol (b), 7HFnol (c), 7,4’DHFnol (d), 5,7DHFnol (e) and 5,7,4’THFnol (f) with UGT 1A1, 1A3, 1A6, 1A7, 1A8, 1A9, 1A10 and 2B7. Flavonols (at 10 μM concentration) were incubated at 37 °C for 1 (or 0.5) hr with UGTs (using optimum final protein concentration ~ 0.25, 0.5 or 1 mg/ml). The amounts of each regiospecific mono-glucuronide formed were measured using UPLC. Rates of mono-glucuronide formation were calculated as nmol/hr/mg of protein. Each bar is the average of three determinations, and the error bars are the standard deviations of the mean (n=3). UGT stands for Uridine diphosphate glucuronosyltransferases).