[Catalytic properties of cholesterol oxidase in the cholesterol oxidation reaction in an aqueous medium].

The effects of organic solvents on cholesterol oxidation by cholesterol oxidase were investigated. It was shown that the increase of isopropanol up to 15% (v/v) in the reaction mixture based on the triethanolamine buffer solution does not influence the value of V, while the Km value for cholesterol shows a bell-shaped dependence and increases more than tenfold within the organic solvent concentration range of about 10%. The changes in the kinetic parameters of the reaction depend not only on the organic solvent concentrations but also on the buffer origin and substrate solution preparation time. This suggests that the composition of the reaction mixture in the first case influences the cholesterol micelle organization which defines its substrate properties in such reactions. Under this stipulation the experimental results can be interpreted within the framework of a new scheme, according to which the specific interaction between cholesterol and delta 4-cholestenon-3 which leads to a decrease of cholesterol mobility and to acceleration of the reaction rate. With a rise in the organic solvent concentration the above-mentioned interactions decelerate, and the enzymatic reaction can be well described by the Michaelis-Menten equation. It is supposed that the cholesterol oxidase-mediated oxidation of cholesterol occurs at the counterface of two phases.