A kinetic and thermodynamic understanding of O2 tolerance in [NiFe]-hydrogenases
A kinetic and thermodynamic understanding of O2 tolerance in [NiFe]-hydrogenases
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DOI：
10.1073/pnas.0905959106
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发表时间：
2009-12-08
影响因子：
11.1
通讯作者：
Armstrong, Fraser A.
中科院分区：
文献类型：
--
作者：
Cracknell, James A.;Wait, Annemarie F.;Armstrong, Fraser A.
在生物学中，H-2的快速氧化和进化是由称为氢化酶的金属酶催化的。这些酶具有不寻常的活性位点，由羰基、氰化物和硫醇盐配体络合的铁组成，通常与镍一起，并且通常被O-2抑制或不可逆地损伤。Knallgas细菌Ralstonia eutropha H16（Re）使用H-2作为能量来源，O-2作为末端电子受体，并且其膜结合摄取[NiFe]-氢化酶（MBH）是“O-2耐受”氢化酶的重要实例。Re MBH的O-2耐受性的机制已通过测量H-2氧化活性在O-2的存在下，在电位，pH值和温度的范围内，并与相同的依赖性进行比较，参与攻击的O-2和随后的活性位点的再活化的各个过程。最重要的是，O-2耐受性随着温度的升高和电位的降低而增加。这些趋势与观察到的再活化动力学的趋势相关，但与H-2亲和力或O-2攻击动力学无关。显然，回收率是一个关键因素。我们提出了一个动力学和热力学模型来解释O-2耐受Re MBH，可以更广泛地应用于其他[NiFe]-氢化酶。
In biology, rapid oxidation and evolution of H-2 is catalyzed by metalloenzymes known as hydrogenases. These enzymes have unusual active sites, consisting of iron complexed by carbonyl, cyanide, and thiolate ligands, often together with nickel, and are typically inhibited or irreversibly damaged by O-2. The Knallgas bacterium Ralstonia eutropha H16 (Re) uses H-2 as an energy source with O-2 as a terminal electron acceptor, and its membrane-bound uptake [NiFe]-hydrogenase (MBH) is an important example of an "O-2-tolerant'' hydrogenase. The mechanism of O-2 tolerance of Re MBH has been probed by measuring H-2 oxidation activity in the presence of O-2 over a range of potential, pH and temperature, and comparing with the same dependencies for individual processes involved in the attack by O-2 and subsequent reactivation of the active site. Most significantly, O-2 tolerance increases with increasing temperature and decreasing potentials. These trends correlate with the trends observed for reactivation kinetics but not for H-2 affinity or the kinetics of O-2 attack. Clearly, the rate of recovery is a crucial factor. We present a kinetic and thermodynamic model to account for O-2 tolerance in Re MBH that may be more widely applied to other [NiFe]-hydrogenases.