Biosynthesis of Gallotannins. ß-Glucogallin-Dependent Galloylation of 1,6-DigaIloylglucose to 1,2,6-Trigalloylglucose

An enzyme from leaves o f sumach ( Rhus typhina) was partially purified that catalyzes the ß-glucogallin (l-O-galloylglucose)-dependent galloylation o f 1,6-digalloylglucose, thus form­ ing 1,2,6-trigalloylglucose and free glucose. This acyltransferase had a molecular weight o f ca. 750,000 and a pH optimum at 5 .0 -5 .5 . Besides ß-glucogallin (Km 3.9 m M ) , also related 1-O-phenylcarboxylglucoses acted as acyl donors. On the other hand, the acceptor substrate, 1,6-digalloylglucose (Km = 0.9 m M ) , could only be replaced by 1,6-diprotocatechuoylglucose (relative activity 46%); however, also tri-, tetra-, and pentagalloylglucoses were galloylated. A pronounced stimulation o f the enzymatic reaction was observed upon addition o f pentaor hexagalloylglucose into the assay mixtures. The systematic name “ß-glucogallin: 1,6-di-O-galloylglucose 2-O-galloyltransferase” (EC 2.3.1. — ) is proposed for the enzyme.