Gallotannin biosynthesis:: β-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 alpha (4)beta (4)-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. (C) 2001 Elsevier Science Ltd. All rights reserved.