Alkaline phosphatase from calf intestinal mucosa in reversed micelle systems: modulation of enzyme membrane activity by pH variation.

The effect of pH variation in aqueous microphases of Aerosol OT (AOT, sodium bis(2-ethylhexyl)sulfosuccinate)/water/octane and brij 96 (oleyl poly(10)oxyethylene ether)/water/cyclohexane reversed micelle (RM) systems on the membrane activity of alkaline phosphatase (AP) from calf intestinal mucosa (EC 3.1.3.1) has been studied. The dependence of enzyme activity on surfactant concentration is observed only for membrane forms of enzymes, and is absent for water soluble forms. In the case of AP, the manifestation of this dependence was governed by the pH of the aqueous microphase of the RM system: it was not observed at the pH-optimum of the enzymatic reaction (pH 10.0-10.5), but appeared at pH below 9.7 and above 10.5. Such behavior may result from the pH-induced change of the enzyme conformation, which according to the fluorescence spectroscopy data takes place in the vicinity of the pH-optimum. This change is probably accompanied by the exposure/masking of an anchor group providing the AP interaction with the RM matrix.