Partial purification and properties of UDP-glucose:vanillate 1- O-glucosyl transferase from oak leaves

Abstract

An enzyme from leaves of red oak ( Quercus rubra) which catalyses the esterification of various phenolic acids with the glucose moiety of UDPG has been purified ca 45-fold. This transferase has a MW of 68 000 and a broad pH optimum of 6.5–7.0. UDP-glucose has been found to act exclusively as the donor molecule. Benzoic acids and, at significantly lower rates, cinnamic acids are utilized as acceptor molecules. The preferred substrates are vanillic acid ( K m = 0.57 mM), veratric acid (0.72 mM), gallic acid (1.11 mM) and p-hydroxybenzoic acid (3.45 mM). Reversibility of the reaction has been demonstrated by the enzymatic formation of UDP-glucose from β-glucogallin (1- O-galloyl-β- D-glucose) and UDP. In spite of the fact that this new enzyme has to be designated, according to its best substrate, as UDP-glucose: vanillate 1- O-glucosyl transferase (EC 2.4.1.—), it is concluded that its physiological role is the formation of β-glucogallin, the putative first intermediate in the biosynthesis of gallotannins.