Isolation and characterisation of two glucosyltransferases from Glycine max associated with bentazone metabolism

Two glucosyltransferases capable of glucosylating the primary major bentazone metabolite, 6‐hydroxybentazone, have been isolated from tolerant soybean (Glycine max (L.) Fiskerby V) tissue. A soluble flavonol glucosyltransferase, whose primary substrate was kaempferol, was isolated from 3‐week‐old light‐grown tissue. This enzyme had a relative molecular mass of 44 600, a pH optimum of 6·3 and Michaelis constants for kaempferol and 6‐hydroxybentazone of 0·09 and 2·45 mM respectively. A membrane‐bound glucosyltransferase whose primary substrate was the intermediate shikimic acid metabolite, p‐hydroxyphenylpyruvic acid, was also isolated from 7‐day‐old etiolated tissue. This enzyme had a relative molecular mass of 53000 (which could be dissociated to approximately 28000), a pH optimum of 7·5 and Michaelis constants for p‐hydroxyphenylpyruvic acid and 6‐hydroxybentazone of 0·11 and 1·96 mM respectively. These results suggest that 6‐hydroxybentazone, and possibly many other hydroxylated pesticides, may be further detoxified by several glucosyltransferases with overlapping specificity whose primary role involves the storage of endogenous metabolites.