Gupta Syamasri, Mukhopadhyay Lana, Moulik S P
Department of Chemistry, Jadavpur University, Kolkata 700 032, India.
Indian J Biochem Biophys. 2003 Oct;40(5):340-9.
The oxidation of beta-D-glucose by the enzyme glucose oxidase was studied in aqueous medium, in solutions of surfactants AOT (2-ethylhexylsulfosuccinate, sodium salt) TX-100 (polyethylene glycol p-tert octyl phenyl ether) and in w/o microemulsion medium (water/AOT/decane) at different water/AOT mole ratio (omega), pH, temperature and in presence of additives. 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, kcat values exhibited a deformed W-shaped profile with omega. At pH 7, a maximum value of kcat was observed at omega = 10.6. The kcat 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 deltaG* was lower, whereas deltaH* and deltaS* were higher in microemulsion than in water. The Michaelis constant, KM was also lower in microemulsion. The inhibition effects of the additives, NaNO3 and NaC were studied in both aqueous and microemulsion media by examining their influences on catalytic constant, kcat and Michaelis constant KM. In microemulsion, both the additives NaNO3 and NaC produced non-competitive inhibition.
在水介质、表面活性剂AOT（2-乙基己基磺基琥珀酸钠）和TX-100（聚乙二醇对叔辛基苯基醚）溶液以及不同水/AOT摩尔比（ω）、pH值、温度且存在添加剂的水包油型微乳液介质（水/AOT/癸烷）中，研究了葡萄糖氧化酶对β-D-葡萄糖的氧化作用。测定了该酶在水介质和微乳液介质中随时间变化的活性。在TX-100和AOT存在下，催化过程受到阻碍。在微乳液介质中，kcat值随ω呈现出变形的W形曲线。在pH值为7时，ω = 10.6时观察到kcat的最大值。发现在pH值为7和8时，微乳液介质中的kcat值均高于水介质中的kcat值。评估了动力学过程的活化参数以及酶-底物米氏复合物的热力学性质。微乳液中的ΔG较低，而ΔH和ΔS*高于水中的相应值。米氏常数KM在微乳液中也较低。通过研究添加剂NaNO3和NaCl对催化常数kcat和米氏常数KM的影响，在水介质和微乳液介质中研究了它们的抑制作用。在微乳液中，添加剂NaNO3和NaCl均产生非竞争性抑制作用。
