| The biocatalysis of commercially purified soybean lipoxygenase (LOX-1B: EC 1.13.11.12) in ternary micellar and neat organic solvent media, using linoleic acid as a substrate model, was investigated. The organic solvent, used throughout this study, was at different ratios in the ternary micellar system, composed of Tris-HCl buffer solution (0.1 M, pH 9.0) and 10 muM of Tween-40 as the surfactant. The results indicated a 1.4- and 1.7-fold increase in LOX activity when, respectively, 2% iso-octane or 2% hexane was used as the organic solvent in comparison to that in the aqueous medium. The kinetic parameters, including Km and Vmax values, the choice of the surfactant, the optimum reaction temperature and the optimum pH, were investigated. The effects of selected parameters, including initial water activity (aw, 0.23 to 0.75), agitation speed (0 to 200 rpm), reaction temperature (20 to 45°C) and thermal stability of LOX activity in neat organic solvent, were also studied. The experimental findings showed that the Km and V max values in the ternary micellar system containing 2% hexane was calculated to be 7.7 mumol of linoleic acid and 30.0 nmol of linoleic acid hydroperoxides (HPODs)/mg protein/min, respectively, as compare to that of 20.7 mumol of linoleic acid and 8.3 nmol HPODs/mg protein/min in the neat organic solvent, respectively. The experimental results indicated that the major LOX specific activity, for both aqueous and ternary micellar systems, was measured at pH 9.0, with a minor one at pH 6.0 for the aqueous system and at pH 7.0 for the ternary micellar system. The activation energy ( Ea) of the reaction system of LOX was 9.87 kJ/mol or 2.36 kcal/mol. The half-life (T50) for LOX was 27.61, 66.63 and 138.6 min for the aqueous, ternary micellar and neat organic media, respectively. |
