Enzymatic Studies on the Reversible Synthesis of Nicotinic Acid-N-glucoside in Heterotrophic Parsley Cell Suspension Cultures

A soluble enzyme catalyzing the transfer of the glucose moiety from UDP-glucose to the nitrogen atom of nicotinic acid was detected in protein preparations from heterotrophic cell suspension cultures of parsley (Petroselinum hortense Hoffm.). Enzyme activity was enriched 22-fold by ammonium sulfate precipitation, gel filtration and ion exchange chromatography. The UDP-glucose : nicotinic acid-N-glucosyltransferase showed a pH-optimum at pH 7.8-8.2 and a temperature optimum at 30 °C. The apparent KM values were determined to be 170 μM for nicotinic acid and 1.2 mM for the cosubstrate. The native enzyme had a molecular mass of about 46 kDa. The glucosyltransferase reaction was shown to be reversible. The transfer of the glucose molecule from nicotinic acid-N-glucoside to uridinediphosphate yielding uridinediphosphoglucose and nicotinic acid could be demonstrated indicating that nicotinic acid-N-glucoside has a high group-transfer potential.