Partial Purification and Some Properties of Flavonol 7-Sulfotransferase from Flaveria bidentis

Abstract

A novel flavonol-specific sulfotransferase was partially purified from the shoot tips of Flaveria bidentis var. Angustifolia O.K. (Asteraceae) by chromatography on 3′-phosphoadenosine 5′-phosphate-agarose affinity column and chromatofocusing on Mono P. The latter step resulted in the separation of two isoforms, both of which exhibited expressed specificity for position 7 of quercetin 3,3′- and quercetin 3,4′-disulfate. The 7-sulfotransferase isoforms I and II had a pH optimum of 7.5 in phosphate buffer, apparent pl values of 6.5 and 6.3, and an M_r of 35,000. They had no requirement for divalent cations and were not inhibited by EDTA or SH group reagents. Their K_m values for both the sulfate donor and flavonol acceptor were of the same order of magnitude (0.20-0.46 micromolar). This enzyme, together with the recently reported flavonol 3-, 3′-, and 4′-sulfotransferases from F. chloraefolia (L Varin, RK Ibrahim [1989] Plant Physiol 90: 977-981) form the complement involved in the biosynthesis of polysulfated flavonols in this genus. A proposed sequential order for the enzymatic sulfation in both species is described.