Beta-glucogallin-tetrakisgalloylglucose O-galloyltransferase () is an enzyme that catalyzes the chemical reaction which transfers the fifth and final gallic acid unit to a central glucose molecule to form the gallotannin, pentagalloylglucose.
The two substrates of this enzyme characterised from oak (Quercus robur) are glucogallin and 1,2,3,6-tetrakis-O-galloyl-β-D-glucose. Its products are D-glucose and pentagalloylglucose. Gallotannins are widely found in foodstuffs.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is 1-O-galloyl-beta-D-glucose:1,2,3,6-tetrakis-O-galloyl-β-D-glucose 4-O-galloyltransferase. Other names in common use include β-glucogallin-tetragalloylglucose 4-galloyltransferase, β-glucogallin:1,2,3,6-tetra-O-galloylglucose, 4-O-galloyltransferase, β-glucogallin:1,2,3,6-tetra-O-galloyl-beta-D-glucose, and 4-O-galloyltransferase.
References