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首页> 外文期刊>International Journal of Biological Macromolecules: Structure, Function and Interactions >THERMAL STABILITY OF ARTEMIA HGPRT - EFFECT OF SUBSTRATES ON INACTIVATION KINETICS
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THERMAL STABILITY OF ARTEMIA HGPRT - EFFECT OF SUBSTRATES ON INACTIVATION KINETICS

机译：HARTRT的热稳定性-基质对失活动力学的影响

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摘要

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT, E.C. 2.4.2.8) from Artemia cysts exhibits maximum activity at 70 degrees C. Its thermal stability has been examined following enzymatic activity as a function of temperature. Cold-induced renaturation experiments of samples heated at increasing temperatures showed that reversibility of thermal inactivation depends on the incubation time and final temperature. Prolonged incubation of the thermoinactivated enzyme at O degrees C did not afford any further increase of the catalytic activity at 37 degrees C. The complex substrate PRPP:Mg protects HGPRT from thermal inactivation. However, incubations with hypoxanthine rendered a less thermostable enzyme at any temperature tested. The irreversible inactivation of HGPRT proceeds in two exponential steps. The analysis of the apparent rate constants for the fast and the slow phases, lambda(1) and lambda(2) as per the Lumry and Eyring model suggests the existence of more than three states in the thermal denaturation pathway of the free enzyme. In the presence of PRPP:Mg the irreversible process follows a single exponential and proceeds very slowly below 70 degrees C. PRPP:Mg also protects the enzyme from inactivation by NEM and pCMB, suggesting that -SH groups may be in the vicinity of the active site. [References: 35]
机译：来自Artemia囊肿的次黄嘌呤-鸟嘌呤磷酸核糖基转移酶（HGPRT，E.C. 2.4.2.8）在70摄氏度下表现出最大的活性。酶活性随温度的变化已研究了其热稳定性。在升高的温度下加热的样品的冷诱导复性实验表明，热灭活的可逆性取决于孵育时间和最终温度。热灭活的酶在O摄氏度下长时间孵育不会在37摄氏度下进一步提高催化活性。复杂的底物PRPP：Mg可保护HGPRT免受热灭活。然而，与次黄嘌呤一起孵育在任何测试温度下均使热稳定性降低。 HGPRT的不可逆灭活分为两个指数步骤。根据Lumry和Eyring模型，对快相和慢相lambda（1）和lambda（2）的表观速率常数的分析表明，游离酶的热变性途径中存在三种以上状态。在存在PRPP：Mg的情况下，不可逆过程遵循单个指数，并且在低于70摄氏度时非常缓慢地进行。PRPP：Mg还可以保护酶免受NEM和pCMB的灭活，这表明-SH基团可能在活性物质附近现场。 [参考：35]

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