Use of borate to control the 5'-position-selective microbial glucosylation of pyridoxine.

Nearly 100% 5'-position selectivity of transglucosylation from maltodextrin to pyridoxine (PN) by cells of Verticillium dahliae TPU 4900 was observed when the reaction was carried out with borate. The same effect of borate was observed not only during synthesis of pyridoxine 5'-alpha-D-glucoside by partially purified enzyme of this strain but also during synthesis of this compound by other microorganisms and with other enzymes (alpha-glucosidase and cyclomaltodextrin glucanotransferase). The effect was thought to be caused by the formation of a borate complex with 3- and 4'-position hydroxyl groups of PN. A decrease in the formation of pyridoxine 5'-alpha-D-glucoside was observed in the reaction with borate, but this decrease was overcome by optimizing the pH and increasing the amount of cells in the reaction mixture.