Stabilization of acid phosphatase in DDDACl/n-butyl acetate reverse micelles

Storage stability of acid phosphatase entrapped in reverse micelles was studied. Supramolecular systems were prepared with a cationic twin chain surfactant, didodecyldimethylammonium chloride (DDDAC1), n-butyl acetate as an organic solvent and different water percentages. The rate of enzyme deactivation was monitored in the temperature interval from 20 to 45 °C, at bulk pH from 4.8 to 6.4, either unstirred conditions or under convective mixing from 250 to 750 rev min-1, water-to-surfactant molar ratio (w0) equal to 11.4, 12.7, 14.2 and with the following buffers, Na-citrate, Li- citrate, K-citrate, Na-propionate. Acid phosphatase entrapped in buffer pools of reverse micelles exhibited enhanced stability in comparison with the enzyme in the pure aqueous phase. Half-life was up to 4 times larger. Both the chemicals used for buffer preparation and buffer pH change, within one unit, were found to influence the rate of acid phosphatase deactivation. The activation energy of enzyme deactivation process in micellar systems was slightly increasing with w0 but the values were not very different from the one in aqueous phase (145.3 kJ mol-1). The rate of deactivation of enzyme confined in the micelles when shear stress was applied was reduced in comparison with that of the free protein, even though the percentage loss was greater.