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首页> 外文期刊>Extremophiles >Thermal stability and biochemical properties of isocitrate dehydrogenase from the thermoacidophilic archaeon Thermoplasma acidophilum
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Thermal stability and biochemical properties of isocitrate dehydrogenase from the thermoacidophilic archaeon Thermoplasma acidophilum

机译：嗜热古生嗜热菌嗜酸嗜热菌中异柠檬酸脱氢酶的热稳定性和生化特性

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Isocitrate dehydrogenase [IDH; EC 1.1.1.42] from the thermoacidophilic archaeon Thermoplasma acidophilum (TaIDH) showed high thermal stability with an apparent melting temperature, T m, of 82.2 and 84.5°C at pH 7.5 and 5.8, respectively. Based on structural alignment of TaIDH with IDH from Aeropyrum pernix (ApIDH) and Archaeoglobus fulgidus (AfIDH) residues forming an aromatic cluster in the clasp-domain thought to strengthen the dimer interface in ApIDH and AfIDH were identified in the former enzyme. Moreover, TaIDH had a shortened N-terminus that may protect the enzyme from thermal denaturation. The enzyme activity of TaIDH was highest at 70°C. The pH-activity profile was bell-shaped with an optimum shifted to a lower pH compared to AfIDH. The activity of TaIDH was influenced by changes in pH with a three-fold reduction in activity when the pH was shifted from the pH-optimum at 7.5 to pH 5.8. However, the specific activity at pH 5.8 was still high when compared with AfIDH. The reduction in activity at pH 5.8 was not due to instability of the enzyme as the T m of TaIDH was higher at pH 5.8 than at 7.5 and the enzyme retained 91% of its activity after incubation at 1 h at pH 5 and 60°C. The difference in the pH-profile of TaIDH in comparison with AfIDH may thus be related to the pK as of their catalytic residues involved in the initial proton abstraction and the final proton donation during the catalysis of oxidative decarboxylation of isocitrate to 2-oxoglutarate and reduced coenzyme.
机译：异柠檬酸脱氢酶[IDH;来自嗜热嗜酸古生菌嗜热嗜热菌（TaIDH）的EC 1.1.1.42]显示出高的热稳定性，在pH 7.5和5.8下的表观熔化温度T m分别为82.2和84.5℃。基于TaIDH与Aeropyrum pernix（ApIDH）和Archaeoglobus fulgidus（AfIDH）的IDH的结构比对，在前一种酶中发现了在扣环结构域中形成芳香簇的残基，认为该残基增强了ApIDH和AfIDH中的二聚体界面。此外，TaIDH的N末端缩短，可以保护酶免受热变性。 TaIDH的酶活性在70℃下最高。与AfIDH相比，pH活性曲线呈钟形，最佳移至更低的pH。当pH从7.5的最佳pH移至5.8时，TaIDH的活性受pH变化的影响，活性降低了三倍。然而，与AfIDH相比，在pH 5.8下的比活性仍然很高。 pH 5.8下活性的降低不是由于酶的不稳定性，因为TaIDH的T msub在pH 5.8下高于7.5，并且在pH 5下孵育1 h后，酶保留了其活性的91％。和60°C。因此，TaIDH与AfIDH相比，pH谱的差异可能与它们在异柠檬酸氧化脱羧反应中获得初始质子提取和最终质子给体时所涉及的催化残基的pKAs有关。 2-氧戊二酸酯和还原型辅酶。

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