Hydroperoxidase activity of lipoxygenase: a kinetic study of isoproterenol oxidation.
The hydroperoxidase activity of soybean lipoxygenase, a non-heme protein, oxidized isoproterenol using H2O2 at pH 6.0. This oxidation was enzymatic, since neither heat-denaturated enzyme or iron ions in the presence of H2O2 produced an increase in absorbance. The initial rate was not linear and showed a characteristic lag period whose length depended on the enzyme and substrate concentration. The lag was decreased if the enzyme and isoproterenol concentration were increased, whereas it increased if the H2O2 concentration was increased. Lipoxygenase showed the typical low specificity for electron donor characteristic of this hydroperoxidase activity (26 mM), but a high affinity for H2O2 (94 microM), although with substrate inhibition (ksi = 3.6 mM). The chemical intermediates produced during the oxidation of isoproterenol were characterized in order to determine the origin of the lag period. A plausible kinetic mechanism is proposed to explain the observed lag period and inhibition by high concentrations of H2O2.
Núñez-Delicado
E
E
Department of Biochemistry and Molecular Biology-A, Faculty of Biology, University of Murcia, Spain.
Pérez-Gilabert
M
M
Sánchez-Ferrer
A
A
García-Carmona
F
F
D004579:Electron Transport; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007545:Isoproterenol / Q000378:metabolism*; D007700:Kinetics; D008084:Lipoxygenase / Q000378:metabolism*; D008956:Models, Chemical; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000378:metabolism; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011489:Protein Denaturation; D013025:Glycine max / Q000201:enzymology*; D013053:Spectrophotometry
D006861:Hydrogen Peroxide; D010544:Peroxidases; D008084:Lipoxygenase; D014442:Monophenol Monooxygenase; D007545:Isoproterenol