β-Glucogallin-Dependent Acyltransferase from Oak Leaves. I. Partial Purification and Characterization

Abstract

Summary An acyltransferase from oak ( Quercus robur ) leaves was purified ca. 50-fold with 20 % yield. As determined with [ 14 C]glucose, this enzyme catalyzes an exchange reaction between β-glucogallin (1- O -galloyl-β-D-glucose) and free glucose, resulting in the formation of labeled substrate. No reaction occurred when glucose was substituted by gallic acid. With the donor molecules benzoyl glucose, p-coumaroyl glucose, and sinapoyl glucose, relative enzyme activities of 195 %, 40 %, and 36 %, respectively, were observed. No reaction was found with the potential substrates β-D-glucose-1-phosphate, α-D-glucose-l-phosphate, D-glucose-6-phosphate, gentiobiose, sucrose, cellobiose, maltose, and trehalose. The transferase has a molecular weight of ca. 380 000, a pH-optimum of 6.6, and a temperature optimum of 30 °C. Neither ammonium ions, divalent cations nor inhibitors acting on SH-groups significantly affect the activity of the enzyme. It is difficult to evaluate to what extent this acyltransferase is related to the biosynthesis and metabolism of gallotannins; at any rate, it provides a convenient tool for the preparation of radioactive β-glucogallin and of related 1- O -acylglucose esters.