Hydroperoxidation of Linoleic Acid Catalysed by Soybean Lipoxygenase

Soybean lipoxygenase-1 (SLO) is often used as the prototype for studying the family of lipoxygenases from tissues of different species. They are non-haem iron dioxygenases that catalyse the conversion of unsaturated fatty acids to hydroperoxides. Plant hpoxygenases 

The interest in the hydroperoxidation of linoleic acid catalysed by SLO, which involves formally the abstraction of a hydrogen atom from the Cll position of the substrate by the Fe(III)-OH cofactor, stems from the fact that it exhibits nearly tanperature-independent rates and kinetic isotope effects (KIEs) close to 80 [28]. This KIE is much higher than that observed in other H-atom abstractions for example, that of the H+Hj versus H-I-D2 hydrogen (deuterium) transfer is only 9.5 1.4 at 30 C [29]. Such high KIEs were claimed to be inconsistent with the TST view of catalysis [30]. 

The isomerisation catalysed by TIM and the hydroperoxidation catalysed by SLO follow very different mechanisms and are subject to different stabilisation factors. Nevertheless, they show that Pauling s view of enzyme catalysis remains very influential, in particular his implication of the role of the enzyme in the stabilisation of the transition state of the rate-determining step. In modem words, this has been stated as the entire and sole source of the catalytic power of enzymes is due to the lowering of the free energy of activation and any increase in the generalised transmission coefficient, as compared to that of the uncatalysed reaction [35]. Of the factors contributing to the transmission coefficient, tunnelling is decidedly the most important one. 

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Hydroperoxidation of Linoleic Acid Catalysed by Soybean Lipoxygenase-1... 

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