Kinetics in microemulsion V. Glucose oxidase catalyzed oxidation of β-D-glucose in aqueous, micellar and water-in-oil microemulsion media

摘要

The oxidation of β-D-glucose by the enzyme glucose oxidase was studied in aqueous medium, in solutions of surfac-tants AOT (2-ethylhexylsulfosuccinate, sodium salt) TX-100 (polyethylene glycol p-tert octyl phenyl ether) and in w/o mi-croemulsion medium (water/AOT/decane) at different water/AOT mole ratio (ω), pH, temperature and in presence of addi-tives. The time-dependent activities of the enzyme in aqueous and microemulsion media were determined. The catalytic process was retarded in the presence of TX-100 and AOT. In microemulsion medium, ksubcat/sub values exhibited a deformed W-shaped profile with ω. At pH 7, a maximum value of ksubcat/sub was observed at ω = 10.6. The ksubcat/sub values were found to be higher in microemulsion medium than in aqueous medium at both pH’s 7 and 8. Activation parameters for the kinetic process were evaluated together with the thermodynamics of the enzyme-substrate Michaelis complex. The ΔG* was lower, whereas ΔH* and ΔS* were higher in microemulsion than in water. The Michaelis constant, KsubM/sub was also lower in microemulsion. The in-hibition effects of the additives, NaNOsub3/sub and NaC were studied in both aqueous and microemulsion media by examining their influences on catalytic constant, ksubcat/sub and Michaelis constant KsubM/sub. In microemulsion, both the additives NaNOsub3/sub and NaC produced non-competitive inhibition.