Siebenlist K R, Taketa F
Biochemistry. 1983 Aug 30;22(18):4229-34. doi: 10.1021/bi00287a011.
Triethyltin bromide was found to demonstrate temperature-dependent inactivation of yeast hexokinase B. At temperatures of 20 degrees C or lower, little or no inactivation of the enzyme was detected after 2 h of reaction with 50-300 microM concentrations of the reagent. However, incubation at 25 degrees C or higher resulted in an increased rate and extent of loss of the enzyme activity with increasing incubation temperatures. The Arrhenius plot for the inactivation process showed a sharp break at approximately 30 degrees C, with a heat of activation (delta H*) above this temperature of 55.2 kcal, indicating that a triethyltin-induced conformational change occurred at the elevated temperatures. Sugar substrates provided protection against the inactivating effect by reducing the binding of triethyltin to the enzyme. In the absence of glucose, two sites of different affinity for triethyltin exist in the hexokinase monomer. Binding of triethyltin to the enzyme shifted its monomer-dimer equilibrium toward the monomeric form in an early stage of the interaction. Inactivation of the enzyme was associated with a slower subsequent event. Comparative effects of various organotin compounds on the activity of the enzyme indicated that inhibitory potency was associated with increasing hydrophobicity of the alkyl groups attached to the tin.
发现溴化三乙锡对酵母己糖激酶B表现出温度依赖性失活作用。在20摄氏度或更低温度下，用50 - 300微摩尔浓度的该试剂反应2小时后，未检测到该酶有明显失活或几乎没有失活。然而，在25摄氏度或更高温度下孵育，随着孵育温度升高，酶活性丧失的速率和程度增加。失活过程的阿累尼乌斯曲线在约30摄氏度处出现明显转折，高于此温度的活化热（ΔH*）为55.2千卡，这表明在较高温度下发生了三乙锡诱导的构象变化。糖类底物通过减少三乙锡与酶的结合来提供对失活作用的保护。在没有葡萄糖的情况下，己糖激酶单体中存在两个对三乙锡亲和力不同的位点。在相互作用的早期阶段，三乙锡与酶的结合使其一聚体 - 二聚体平衡向单体形式移动。酶的失活与随后较慢的事件有关。各种有机锡化合物对该酶活性的比较效应表明，抑制效力与连接在锡上的烷基疏水性增加有关。
