ACTIVITY AND SPECTROSCOPIC PROPERTIES OF BOVINE LIVER CATALASE IN SODIUM BIS(2-ETHYLHEXYL)SULFOSUCCINATE ISOOCTANE REVERSE MICELLES

Spectroscopic properties such as ultraviolet-visible spectroscopy, cir cular dichroism, steady state fluorescence and the catalatic activity of bovine liver catalase (BLC) have been studied in reverse-micelles m icroemulsions formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) i n isooctane. Activity measurements were carried out with the highly wa ter soluble hydrogen peroxide as substrate as a function of temperatur e and pH, at various concentrations of substrate, enzyme, AOT and at d ifferent w0 values (w0 = [H2O]/[AOT]). The folding of catalase in reve rse micelles is not drastically altered, although there are changes in the local surrounding of the prosthetic group. Kinetic measurements h ave been carried out under first-order conditions at low substrate con centration. They indicate that the measured substrate decomposition ra te is limited by the exchange of substrate molecules between the subst rate-filled and the enzyme-containing micelles. The specificity consta nt, k(s) = k(cat)/K(M), as related to water pool concentrations, k(s,w p)rm was, at all w0 values, considerably lower than k(s) measured in b uffer (k(s)b). In contrast, overall values of k(s) in reverse micelles , k(s,ov)rm, were always 2-4-times higher than k(s)b. This apparent su peractivity can, however, be ascribed to concentration effects. No 'be ll-curve' to describe the w0 dependence of catalase activity in revers e micelles was found, k or k(s) increasing monotonously up to w0 = 50.