Oxygen concentration determines regiospecificity in soybean lipoxygenase-1 reaction via a branched kinetic scheme.
The effect of oxygen concentration on the regiospecificity of the soybean lipoxygenase-1 dioxygenation reaction was studied. At low oxygen concentrations (<5 microM), a dramatic change in the regiospecificity of the enzyme was observed with the hydroperoxy-octadecadienoic acid (HPOD) 13:9 ratio closer to 50:50 instead of the generally reported 95:5. This alteration of regiospecificity is not an isolated phenomenon, since it occurs during a reaction carried out under "classical" conditions, i.e. in a buffer saturated with air before the reaction. beta-carotene bleaching and electronic paramagnetic resonance findings provided evidence that substrate-derived free radical species are released from the enzyme. The kinetic scheme proposed by Schilstra et al. (Schilstra, M. J., Veldink, G. A. & Vliegenthart, J. F. G. (1994) Biochemistry 33, 3974-3979) was thus expanded to account for the observed variations in specificity. The equations describing the branched scheme show two different kinetic pathways: a fully enzymatic one leading to a regio-isomeric composition of 13-HPOD:9-HPOD = 95:5, and a semienzymatic one leading to a regio-isomeric composition of 13-HPOD:9-HPOD = 50:50. The ratio between the two different pathways depends on oxygen concentration, which thus determines the overall specificity of the reaction.
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Laboratory of Enzyme Technology, UPRES A 6022 CNRS, University of Compiègne, B.P. 20.529, 60205 Compiègne, France.
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D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy; D007536:Isomerism; D019787:Linoleic Acid / Q000378:metabolism; D008041:Linoleic Acids / Q000378:metabolism; D008054:Lipid Peroxides; D008084:Lipoxygenase / Q000378:metabolism*; D008956:Models, Chemical; D010100:Oxygen / Q000494:pharmacology*; D011199:Potentiometry; D013025:Glycine max / Q000201:enzymology*; D013379:Substrate Specificity / Q000187:drug effects; D019207:beta Carotene / Q000378:metabolism
D008041:Linoleic Acids; D008054:Lipid Peroxides; D019207:beta Carotene; C038649:13-hydroperoxy-9,11-octadecadienoic acid; C049606:9-hydroperoxy-11,12-octadecadienoic acid; D019787:Linoleic Acid; D008084:Lipoxygenase; D010100:Oxygen