Gallotannin biosynthesis: A new beta-glucogallin-dependent galloyltransferase from sumac leaves acylating gallotannins at positions 2 and 4

Leaves of staghorn sumac (Rhus typhina) contain several isoenzymes that cat alyze the beta-glucogallin (1-O-galloyl-beta-D-glucose)-dependent transform ation of 1,2,3,4,6-penta-O-galloyl-beta-D-glucose to complex gallotannins. Among these, a new galloyltransferase has been isolated that preferentially acylated the 4-position of the substrate, followed by substitution of the 2-position, thus yielding the hexa-galloylglucose, 4-O-digalloyl-1,2,3,6-te tra-O-galloyl-beta-D-glucose, and the heptagalloylglucose, 2,4-di-O-digallo yl-1,3,6-tri-O-galloyl-beta-D-glucose. The enzyme, for which a M-r value of 360,000 was determined by gel filtration, was purified more than 500-fold to apparent homogeneity and was most reactive with hexagalloylglucose as ac ceptor substrate. The transferase had a pH optimum at 4.8, an isoelectric p oint at pH 4.95, was stable between pH 3.7 and 6.8, and proved comparativel y heat-stable as shown by a temperature optimum of 40 degrees C and a half- maximal activity at 64 degrees C.