Kinetics of bilirubin oxidation catalysed by bilirubin oxidase in a water-in-oil microemulsion system.
1. Bilirubin oxidase can catalyse the oxidation of its primary substrate, bilirubin, in a water-in-oil microemulsion, which consists of discrete nanometer-diameter water droplets dispersed in a continuous water-immiscible oil medium. The droplets are stabilized by a monolayer of the surfactant, cetyltrimethylammonium bromide present at the oil/water interface. 2. Spectroscopic evidence is presented to show that bilirubin solubilized in this system is located mainly in the surfactant layer, in a form accessible to the enzyme molecule. 3. Studies are presented on the enzyme-catalysed rate of bilirubin oxidation in this system, as a function of temperature, pH, water content, and substrate and enzyme concentrations. 4. The main conclusions are that the enzyme can efficiently oxidise bilirubin in microemulsions of low water content. The reaction obeys Michaelis-Menten kinetics. The optimal pH for the catalysis is 8.0. The efficiency of catalysis decreases sharply as the water content increases.
Biological Laboratory, University of Kent, Canterbury, England.
C
C
Oldfield
R B
RB
Freedman
D001663:Bilirubin / Q000378:metabolism*; D001664:Biliverdine / Q000378:metabolism; D000077286:Cetrimonium; D002593:Cetrimonium Compounds; D002725:Chloroform; D003902:Detergents; D004655:Emulsions; D006536:Heptanes; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D012995:Solubility; D013053:Spectrophotometry; D014867:Water
D002593:Cetrimonium Compounds; D003902:Detergents; D004655:Emulsions; D006536:Heptanes; D014867:Water; C028618:n-heptane; D002725:Chloroform; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C042401:bilirubin oxidase; D001664:Biliverdine; D001663:Bilirubin; D000077286:Cetrimonium