FACTORS AFFECTING ENZYME CHARACTERISTICS OF BILIRUBIN OXIDASE SUSPENSIONS IN ORGANIC-SOLVENTS

The activity of bilirubin oxidase toward bilirubin was studied in a liquid/solid two-phase low-water organic system using a simple spectrophotometric assay to follow the reaction. The enzyme was lyophilized from aqueous solution before being suspended in the organic solvent reaction medium. The activity was significantly influenced by the properties of the aqueous medium from which the enzyme was lyophilized, specifically its pH, and the quantity and nature of the buffering species. Analysis of these effects showed that the role of buffering species in such systems went beyond their effect in fixing the protonation state of the enzyme. The activity was also influenced by the quantity of water added to the organic solvent reaction medium. The reaction was shown to follow Michaelis-Menten kinetics, and K(m) and k(cat) were determined. The liquid/solid two-phase system studied was extensively compared to a previously studied water-in-oil microemulsion system.