EFFECTS OF HYDRATION DEGREE OF AEROSOL OT REVERSED MICELLES AND CONCENTRATION OF SOLUBILIZED UREASE ON THE STABILITY OF THE ENZYME

The kinetics of urease inactivation in reversed micelles of Aerosol OT (AOT) in octane at 55 degrees C were studied as a function of the ini tial concentration of the enzyme (from 34 to 136 nM) and the hydration degree of the micelles (W-0) To measure initial (A(0)) and residual ( A) activities of urease in AOT micelles and water solutions, we determ ined the rates of urease-catalyzed urea hydrolysis with bromocresol gr een as the pH indicator. The breakpoints observed in the ln(A/A(0))-ti me plots for urease in both media indicate the dissociation-associatio n mechanism of inactivation of oligomeric urease at 55 degrees C and c oncentrations of 34-136 nM. Catalytic activity of urease in micelles ( nu(0)[E](0), sec(-1)) and effective enzyme inactivation rate constant (k(in), sec(-1)) are changed similarly as a function of W-0 and have t heir maxima at W-0 values of 22-23. Increasing the urease concentratio n in AOT reversed micelles in octane and in water solutions stabilizes the enzyme (decreases k(in)) at 55 degrees C.