title: Properties of a Maize Glutathione S-Transferase That Conjugates Coumaric Acid and Other Phenylpropanoids.
abstract: A glutathione S-transferase (GST) enzyme from corn (Zea mays L. Pioneer hybrid 3906) that is active with p-coumaric acid and other unsaturated phenylpropanoids was purified approximately 97-fold and characterized. The native enzyme appeared to be a monomer with a molecular mass of approximately 30 kD and an apparent isoelectric point at pH 5.2. The enzyme had a pH optimum between 7.5 and 8.0 and apparent Km values of 4.4 and 1.9 mM for reduced glutathione (GSH) and p-coumaric acid, respectively. In addition to p-coumaric acid, the enzyme was also active with o-coumaric acid, m-coumaric acid, trans-cinnamic acid, ferulic acid, and coniferyl alcohol. In addition to GSH, the enzyme could also utilize cysteine as a sulfhydryl source. The enzyme activity measured when GSH and trans-cinnamic acid were used as substrates was enhanced 2.6- and 5.2-fold by the addition of 50 [mu]M p-coumaric acid and 7-hydroxycoumarin, respectively. 1H- and 13C-nuclear magnetic resonance spectroscopic analysis of the conjugate revealed that the enzyme catalyzed the addition of GSH to the olefinic double bond of p-coumaric acid. Based on the high activity and the substrate specificity of this enzyme, it is possible that this enzyme may be involved in the in vivo conjugation of a number of unsaturated phenylpropanoids.
authors.affiliation: Department of Biological Sciences, DePaul University, Chicago, Illinois 60614 (J.V.D., T.P.D., L.E.O.).
authors.forename: J. V.
authors.initials: JV
authors.lastname: Dean
authors.forename: T. P.
authors.initials: TP
authors.lastname: Devarenne
authors.forename: I. S.
authors.initials: IS
authors.lastname: Lee
authors.forename: L. E.
authors.initials: LE
authors.lastname: Orlofsky