Partial Purification and Properties of an Inducible Uridine 5′-Diphosphate-Glucose-Salicylic Acid Glucosyltransferase from Oat Roots

A salicylic acid (SA)-inducible uridine 5'-diphosphate (UDP)-glucose:SA 3-O-glucosyltransferase was extracted from oat (Avena sativa L. cv Dal) roots. Reverse phase high-performance liquid chromatography or anion exchange chromatography was used to separate SA from the product, beta-O-d-glucosylsalicylic acid. The soluble enzyme was purified 176-fold with 5% recovery using a combination of pH fractionation, anion exchange, gel filtration, and chromatofocusing chromatography. The partially purified protein had a native molecular weight of about 50,000, an apparent isoelectric point at pH 5.0, and maximum activity at pH 5.5. The enzyme had a K(m) of 0.28 mm for UDP-glucose and was highly specific for this sugar donor. More than 20 hydroxybenzoic and hydroxycinnamic acid derivatives were assayed as potential glucose acceptors. UDP-glucose:SA 3-O-glucosyltransferase activity was highly specific toward SA (K(m) = 0.16 mm). The enzyme was inhibited by UDP and uridine 5'-triphosphate but not by up to 7.5 mm uridine 5'-monophosphate.