Gallotannin biosynthesis: beta-glucogallin: hexagalloyl 3-O-galloyltransferase from Rhus typhina leaves.

Leaves of staghorn sumac (Rhus typhina) contain several galloyltransferases that catalyze the beta-glucogallin dependent transformation of 1,2,3,4,6-pentagalloylglucose to gallotannins. Among these, an enzyme has been isolated that preferentially acylates the 3-position of the hexagalloylglucose, 3-O-digalloyl-1,2,3,4,6-tetra-O-galloylglucose, to afford the corresponding heptagalloylglucose being characterized by a 3-O-meta-trigalloyl side-chain. The enzyme, for which a M(r) of ca. 260,000 was determined, was purified to apparent homogeneity. SDS-PAGE suggested an alpha4beta4-conformation of the native enzyme. It had a pH-optimum and an isolelectric point at pH 5.6, was most stable at pH 4.0-4.3, and displayed excellent heat-stability and in particular an extreme cold-tolerance. We propose the systematic name "beta-glucogallin: hexagalloylglucose 3-O-galloyltransferase" for this new enzyme.