title: Biochemical characterization of the dual positional specific maize lipoxygenase and the dependence of lagging and initial burst phenomenon on pH, substrate, and detergent during pre-steady state kinetics.
abstract: The wound-inducible lipoxygenase obtained from maize is one of the nontraditional lipoxygenases that possess dual positional specificity. In this paper, we provide our results on the determination and comparison of the kinetic constants of the maize lipoxygenase, with or without detergents in the steady state, and characterization of the dependence of the kinetic lag phase or initial burst, on pH, substrate, and detergent in the pre-steady state of the lipoxygenase reaction. The oxidation of linoleic acid showed a typical lag phase in the pre-steady state of the lipoxygenase reaction at pH 7.5 in the presence of 0.25% Tween-20 detergent. The reciprocal correlation between the induction period and the enzyme level indicated that this lag phenomenon was attributable to the slow oxidative activation of Fe (II) to Fe (III) at the active site of the enzyme as observed in other lipoxygenase reactions. Contrary to the lagging phenomenon observed at pH 7.5 in the presence of Tween-20, a unique initial burst was observed at pH 6.2 in the absence of detergents. To our knowledge, the initial burst in the oxidation of linoleic acid at pH 6.2 is the first observation in the lipoxygenase reaction. Kinetic constants (K(m) and k(cat) values) were largely dependent on the presence of detergent. An inverse correlation of the initial burst period with enzyme levels and interpretations on kinetic constants suggested that the observed initial burst in the oxidation of linoleic acid could be due to the availability of free fatty acids as substrates for binding with the lipoxygenase enzyme.
authors.affiliation: Department of Molecular Biotechnology, Agricultural Plant Stress Research Center, Biotechnology Research Institute, College of Agriculture and Life Sciences, Chonnam National University, Kwangju 500-757, Republic of Korea.
authors.forename: Kyoungwon
authors.initials: K
authors.lastname: Cho
authors.forename: Sungkuk
authors.initials: S
authors.lastname: Jang
authors.forename: Thavrak
authors.initials: T
authors.lastname: Huon
authors.forename: Sangwook
authors.initials: S
authors.lastname: Park
authors.forename: Oksoo
authors.initials: O
authors.lastname: Han
mesh_terms: D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019787:Linoleic Acid / Q000378:metabolism; D008084:Lipoxygenase / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D011136:Polysorbates / Q000494:pharmacology*; D013379:Substrate Specificity; D013997:Time Factors; D003313:Zea mays / Q000201:enzymology*
chemical_list: D011136:Polysorbates; D019787:Linoleic Acid; D008084:Lipoxygenase