FINDING OF UDP-GLUCOSE - NICOTINIC ACID-N-GLUCOSYLTRANSFERASE ACTIVITY IN CULTURED TOBACCO CELLS AND ITS PROPERTIES

We have already identified N-(beta-D-glucopyranosyl)nicotinic acid, wh ich,vas isolated from cultured tobacco cells, as a novel niacin metabo lite, The enzyme activity for the biosynthesis of this compound, UDP-g lucose: nicotinic acid-N-glucosyltransferase, was found in cell-free e xtracts from cultured cells of tobacco (Nicotiana tabacum XD-6) and pr operties were investigated in this experiment, The general catalytic p roperties were as follows: optimum temperature was 25 degrees C, optim um pH was 6.1, the K-m for NiA and UDP-glucose were calculated at 220 mu M and 4.3 mM, respectively, The enzyme activity was lowered by heav y metal ions, isonicotinic acid, benzoic acid, and 6-hydroxynicotinic acid, The roles of niacin metabolites in cultured tobacco cells are di scussed in relation to the enzyme.