PARTIAL-PURIFICATION AND CHARACTERIZATION OF ARABIDOPSIS-THALIANA UDPG-THIOHYDROXIMATE GLUCOSYLTRANSFERASE

UDPG:thiohydroximate glucosyltransferase (EC 2.4.1.-), which catalyses the penultimate reaction in glucosinolate biosynthesis, was purified 1100-fold in 37% yield from Arabidopsis thaliana inflorescences. The enzyme possessed a native M(r) of 57 800 and a pi of 4.5. At its optimum pH of 6.0, it showed a K-m for UDPG of 0.27 mM. Enzyme activity was stimulated 20-45% by thiol reducing agents (e.g. 2-mercaptoethanol, L-cysteine), CaCl2, MgCl2 and MnCl2, but was greatly inhibited by ZnCl2 and CuCl2. With the exception of 1,10-phenanthroline (10 mM) which caused ca 50% inhibition, metal chelators had little effect upon glucosyltransferase activity. The sensitivity of the enzyme to several thiol blocking reagents suggests that sulphydryl groups are essential for GT activity. The purified Arabidopsis enzyme preparation lacked desulphoglucosinolate sulphotransferase activity.