摘要
根据土壤脲酶动力学参数与温度的关系，借助于经典酶学理论，较为系统地研究了陕西水稻土、褐土、蝼土脲酶的热力学特征。结果表明，将整个酶促反应划分为酶-底物复合物形成和分解两个阶段分别计算其热力学函数是可行的，得到了更多酶促反应机理方面的信息；不同土样脲酶复合物形成和分解阶段的温度系数Q10、活化能Ea、活化焓△H、活化熵△S和活化自由能△G有明显差异；土壤脲酶的Q10范围为0．82～2．48；两阶段土壤脲酶除个别处理外Ea、△H1、△H2、△S均大于零，揭示出形成和分解阶段酶促反应的有序性较差，混乱度较大，需要外界提供更多能量来完成酶活性部位与反应物的互补契合以及解离，最终完成酶促反应；形成阶段△G1和整个反应的△G、△H均小于零，表明形成阶段和整个酶促反应为一可自发进行的放热反应，总体上不需要外界能量即可完成；各土样分解阶段的△G2均大于零，表明土壤类型、肥力状况等对酶促反应的复合物分解过程的可能性无显著影响，复合物分解是酶促反应的限速步骤。可见得到的热力学参数从多方面共同表征了各土样酶促反应机理上的细微差异。
Thermodynamic characteristics of urease in four Shaanxi soils （Hap-stagnic Anthrosds, Cal-Ustic Luvisols and Eum-Orthic Anthrosols） were systematically studied based on the relationship between kinetic parameters of soil urease and temperature, and classical enzymological theory. Results show that enzyme-catalyzed reaction could be divided into two steps, namely, formation of enzyme-substance complex （ES） and dissociation of the ES, of which the thermodynamic functions could thus be calculated, separately, and more information obtained of the mechanism of the enzyme-catalyzed reaction. The four soil samples differed significantly in temperature coefficient Q10, activation energy Ea, enthalpy of activation △H, activation entropy △S and activation free energy △G, in the two steps. Q10 of the soil urease ranged between 0.83 to 2.48, lower than the Q10 in normal chemical reactions. The values of Ea, △H1, △H2 and △S of the soil urease in both steps were all positive except for in some individual treatments, suggesting more confusion and less ordering of the reaction, which means that more external energy is needed to complete the enzyme catalyzed reaction. The △G1 in the step of ES formation and the △G and △H of the enzyme reaction were all negative, indicating that ES formation and the entire enzyme catalyzed reaction is a spontaneous, heat-releaslng process. The △G2 of ES dissociation was positive with no difference between samples, which means that type and fertility of the soils had minor influence on this reaction. It was also verified that the ES dissociation was a rate-limiting step of the reaction. This work provides a better understanding of the subtle differences in mechanisms of the enzyme-catalyzed reactions between different soils.
出处
《土壤学报》
CAS
CSCD
北大核心
2007年第6期1043-1048,共6页
Acta Pedologica Sinica
基金
国家自然科学基金项目(40301022)
沈阳环境工程重点实验室项目和国家教委博士点基金资助
关键词
热力学特征
土壤脲酶
陕西土壤
Thermodynamic characteristics
Soil urease
Shaanxi soils
