Surfactant inhibition of cholesterol oxidase.

Little is known of the effect of surfactants upon the activity of cholesterol oxidase. This study demonstrates the interrelationship of surfactant, enzyme and substrate, and illustrates a possible source of inaccuracy within an enzymatic cholesterol assay. Using the rate at which cholesterol is converted to delta 4-cholestenone, the reaction was followed directly bby monitoring the increase in absorbance at 240 nm. Inhibition of cholesterol oxidase was demonstrated with three surfactants, hydroxypolyethoxydodecane, Tween 20 and Triton-X-405. A fourth, Triton-X-100, produced high enzyme activity, although low concentrations resulted in incomplete substrate dispersal and high concentrations caused high blank values. Hydroxypolyethoxyduodecane was studied more closely and the mechanism of inhibition is suggested as poor substrate dispersal at low surfactant concentration and a competitive inhibition at higher concentrations.