7-OH-flavone is sulfated in the human liver and duodenum, whereas 5-OH-flavone and 3-OH-flavone are potent inhibitors of SULT1A1 activity and 7-OH-flavone sulfation rate. Xenobiotica. 2002 Jul;32(7):563-71

1. The aim of this investigation was to see whether 7-OH-¯avone, 5-OH-¯avone and 3-OH-¯avone, which are present in edible vegetables, fruit and wine, are substrates or inhibitors of human liver and duodenum sulfotransferase. 2. An assay was set up to study the sulfation of 7-OH-¯avone, and using this assay, it was observed that 7-OH-¯avone was sulfated and the rate of sulfation (mean SD) was 324 87 pmol min¡1 mg¡1 (liver) and 584 164 pmol min¡1mg¡1 (duodenum; p < 0:0001). 3. 7-OH-¯avone sulfotransferase followed Michaelis±Menten kinetics and the Km (mean SD) was 0.2 0.04 mM (liver) and 1.1 0.3 mM (duodenum; p ˆ 0:008). Vmax (mean SD) was 392 134 pmol min¡1 mg¡1 (liver) and 815 233 pmolmin¡1 mg¡1 (duodenum; p ˆ 0:016). 4. 5-OH-¯avone and 3-OH-¯avone were not sulfated and were inhibitors of human liver and duodenum SULT1A1 activity and 7-OH-¯avone sulfation rate. 5. The IC50 of 5-OH-¯avone for SULT1A1 was 0.3 0.06 mM (liver) and 0.3 0.1 mM (duodenum; n.s.) and those of 3-OH-¯avone were 1.0 0.1 mM (liver) and 1.6 0.03 mM (duodenum; p ˆ 0:0006). 6. There was inhibition of 7-OH-¯avone sulfation rate by 5-OH-¯avone and 3-OH- ¯avone. The IC50 of 5-OH-¯avone for the sulfation rate of 7-OH-¯avone was 3.5 0.5 mM (liver) and 69 18 mM (duodenum; p < 0:0001) and for 3-OH-¯avone it was 18 3.4 mM (liver) and 213 47 mM (duodenum; p < 0:0001). 7. The position of the hydroxy group confers to the molecules of OH-¯avones the quality of substrate or inhibitor of sulfotransferase.