The effects of Brij30 concentration on the stabilities and activities of yeast alcohol dehydrogenase (YADH) at various ω0 values have been studied. Generally, the residual activity of YADH decreased rapidly first and then approached to a steady value. By the addition of Brij30, it was found that the stability of YADH could be enhanced significantly at ω0=10. However, at ω0=20, the stability of YADH was not remarkably improved and under some conditions was even lower than that in the absence of Brij30. By the investigation on the hydrodynamic diameter of mixed reverse micelles and its distribution via dynamic light scattering, it was suggested that the structure of mixed reverse micelles and the stability of YADH were determined by four important factors, including the surface charge density, bound water, reverse micellar size, and the entrapment of water by hydrophilic-hydrophilic interaction of Aerosol OT (AOT) and Brij30. The effects of these four factors on the stability of YADH at various ω0 values and Brij30 concentration have been discussed in detail. When they were reduced, the stability of YADH might be improved. In addition, it was found that the activity of YADH in AOT/Brij30 mixed reverse micelles might be enhanced at appropriate Brij30 concentrations and ω0 values. According to the hydrodynamic diameter of mixed reverse micelles and its distribution, three main factors were suggested. They were the hydrophobic and electrostatic interactions between enzyme and surfactants, the reverse micellar size, and the bound degree of water molecules. An optimal reverse micellar size and the reductions of the other two factors would lead to the enhancement of enzyme activity.
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