EFFECT OF SURFACTANT NATURE ON UREASE STABILITY IN REVERSED MICELLAR SYSTEMS

The effective inactivation constants (k(in)) were calculated from semi logarithmic plots of urease inactivation at 55 degrees C in reversed m icelles of anion aerosol OT (AOT) in octane, cationic cetyl-trimethyla mmonium bromide (CTAB) in octane with 15% hexanol, and in mixed micell es of AOT-Triton X-100 (1:1) and CTAB-Triton X-100 (1:1) in octane wit h 5 or 15% hexanol. The effect of the initial urease concentration (34 -136 nM) and hydration degree w(0) of all four micellar systems on the k(in) values was studied at 55 degrees C. In all micellar systems inc rease of concentration of solubilized urease caused significant decrea se in k(in). In AOT micelles in octane the dependence of k(in) on w(0) has a maximum at hydration degree 20; this corresponds to the maximal catalytic activity of urease. In three other micellar systems k(in) v alues gradually decreased with increasing w(0), i.e., micelle moisteni ng stabilizes urease. The enzyme stability in the system AOT-Triton X- 100 was twofold higher than in aqueous medium. The temperature depende nces of excess heat capacity of urease were determined by differential scanning calorimetry and compared with curves of heat consumption of the enzyme in aqueous medium. Urease structure in less stable and less cooperative in reversed AOT micelles (w(0) = 20) than in aqueous solu tion. The dissociation-association scheme of urease inactivation is di scussed.