Open AccessKinetics of bilirubin oxidation catalysed by bilirubin oxidase in a water‐in‐oil microemulsion system
Author(s) -
OLDFIELD Christopher,
FREEDMAN Robert B.
Publication year - 1989
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1989.tb14935.x
Subject(s) - chemistry , bilirubin oxidase , microemulsion , pulmonary surfactant , substrate (aquarium) , catalysis , kinetics , monolayer , bilirubin , inorganic chemistry , organic chemistry , chemical engineering , enzyme , biochemistry , oceanography , physics , quantum mechanics , engineering , geology , medicine , gastroenterology
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.