陕西土壤脲酶热力学特征研究
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* 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


THERMODYNAMIC CHARACTERISTICS OF UREASE IN SOILS OF SHAANXI PROVINCE
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    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、土脲酶的热力学特征。结果表明,将整个酶促反应划分为酶2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ΔH、活化熵ΔS和活化自由能ΔG有明显差异;土壤脲酶的Q10范围为0182~2148;两阶段土壤脲酶除个别处理外Ea、ΔH1、ΔH2、ΔS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ΔG1和整个反应的ΔG、ΔH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ΔG2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。

    Abstract:

    Thermodynamic characteristics of urease in four Shaanxi soils (Hapstagnic 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 ΔH,activation entropy ΔS and activation free energy ΔG,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,ΔH1H2 and ΔS 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 ΔG1 in the step of ES formation and the ΔG and ΔH of the enzyme reaction were all negative,indicating that ES formation and the entire enzyme catalyzed reaction is a spontaneous,heatreleasing process.The ΔG2 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 ratelimiting step of the reaction.This work provides a better understanding of the subtle differences in mechanisms of the enzyme-catalyzed reactions between different soils.

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和文祥,朱铭莪,张一平,孙铁珩.陕西土壤脲酶热力学特征研究[J].土壤学报,2007,44(6):1043-1048. DOI:10.11766/trxb200607270612 He Wenxiang, Zhu Ming'e, Zhang Yiping, Sun Tieheng. THERMODYNAMIC CHARACTERISTICS OF UREASE IN SOILS OF SHAANXI PROVINCE[J]. Acta Pedologica Sinica,2007,44(6):1043-1048.

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  • 收稿日期:2006-07-27
  • 最后修改日期:2006-10-12
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  • 在线发布日期: 2013-02-25
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