Kinetics of soybean lipoxygenase reaction in hydrated reversed micelles

The rate of linoleic acid peroxidation catalysed by soybean lipoxygenase I was studied as a function of the hydration degree of aerosol OT (bis(2-ethylhexyl) sulfosuccinate sodium salt) reversed micelles in octane. Lipoxygenase reaction parameters for the micelle-bound substrate were spectrophotometrically determined. The linoleic acid distribution between the micelles and octane was detected by the sedimentation method, with the concentration of linoleic acid in supernatant after settling of micelles (i.e. the concentration of free linoleic acid) being estimated by the enzymatic method. The apparent constant of linoleic acid distribution (the ratio of the bound and free substrate concentrations) was enhanced with increasing hydration of reversed micelles. The dependence of the enzymatic reaction rate on the bound substrate concentration obeyed the empiric Hill equation. The Hill coefficient remained practically constant (h = 1.34) as the hydration degree changed. Parameters of the lipoxygenase reaction, enzyme reaction limiting rate V and semi-saturation substrate concentration [S]0.5 increased with increasing degree of hydration and reached the optimum at [H2O]/[AOT] approximately 30, where dimensions of the micellar internal cavity coincided with those of the enzyme molecule. Some aspects of kinetic behavior of membrane-bound enzymes participating in chemical transformation of non-polar compounds dispersed in lipid phase are discussed.