Elucidating the Molecular Mechanism of a Ni Hydrogenase: An Infrared Spectroscopic Approach

本研究详细介绍了利用静态和时间分辨傅立叶变换红外光谱来描述Ni氢化酶中氢结合和活化的分子机制。研究目标是：(1)确定2100 ~ 1900 cm-1之间的异常红外波段是否为Ni氢化酶的一般特征。为此目的，将对一种具有良好特征的千兆脱硫弧菌的氢化酶进行一系列红外研究。(2)利用红外光谱技术，结合酶的化学修饰和同位素标记酶的研究，鉴定了产生这些不寻常红外特征的结构。(3)利用三种红外特征进一步研究酶的各种氧化还原状态。这种方法提供了一个独特的机会；镍氢化酶显示出至少两种epr沉默物种，它们在2100和1900 cm-1光谱区域的红外特征可以区分。(4)利用中红外光谱研究单个氨基酸在氢活化中的作用。(5)酶在不同氧化还原状态下Ni中心氧化态的检测。这种方法使用了由Ni结合的一氧化碳产生的红外可探测一氧化碳拉伸频率，作为Ni氧化态的探针。氢化酶是催化自然界中最简单的反应和最简单的将电能转化为通用的化学能的酶：2e- + 2H+ = H2。本研究包括对这些酶特有的异常红外吸收带进行光谱研究。利用红外光谱研究了千兆Desulfovibrio gigas中表征良好的Ni氢化酶。预计这项工作将对理解Ni氢化酶将氢分子分裂成质子和电子的能力的机制产生重要影响。这项工作还涉及在严格厌氧条件下处理红外样品的方法的发展，并且应该证明在其他氧敏感金属蛋白的红外研究中的普遍效用。＊＊＊

9509064 Bagley This research details the utilization of static and time resolved Fourier transform infrared spectroscopy for delineating the molecular mechanism of hydrogen binding and activation in Ni hydrogenases. The research objectives are: (1) Determination of whether the anomalous infrared bands detected between 2100 and 1900 cm-1 are general features of Ni hydrogenases. To this end a series of infrared studies will be carried out on a well-characterized hydrogenase from Desulfovibrio gigas. (2) Identification of the structure responsible for these unusual infrared signatures using infrared spectroscopy coupled with chemical modification of the enzyme and the study of isotopically labeled enzyme. (3) Utilization of the three infrared signatures for further study of the various redox states of the enzyme. This approach provides a unique opportunity; Ni hydrogenases display at least two EPR-silent species which are distinguishable by their infrared signatures in the 2100 and 1900 cm-1 spectral region. (4) Utilization of mid- infrared spectroscopy to examine the role individual amino acids play in the activation of hydrogen. (5) Examination of the oxidation state of the Ni center in various redox states of the enzymes. This approach used the infrared detectable carbon monoxide stretching frequency, arising from Ni bound carbon monoxide, as a probe of the oxidation state of the Ni. %%% Ni Hydrogenases are enzymes that catalyze the simplest reaction in nature and the simplest conversion of electrical energy into chemical energy of universal utility: 2e- + 2H+ = H2. This research involves a spectroscopic study of the anomalous infrared absorption bands that are characteristic of these enzymes. Infrared spectroscopic studies will be made on the well-characterized Ni hydrogenases from Desulfovibrio gigas. It is a anticipated that this work will have important consequences for understanding the mechanism underlying Ni hydrogenase's ability to split molecular hydrogen into protons and electrons. The work also involves the development of methodologies for handling infrared samples under strictly anaerobic conditions, and should prove of general utility in infrared studies of other oxygen sensitive metallo-proteins. ***