Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
J Phys Chem B. 2013 Jan 10;117(1):218-29. doi: 10.1021/jp3121484. Epub 2012 Dec 31.
The mechanism of O(2) reduction by copper amine oxidase from Arthrobacter globiformus (AGAO) is analyzed in relation to the cobalt-substituted protein. The enzyme utilizes a tyrosine-derived topaquinone cofactor to oxidize primary amines and reduce O(2) to H(2)O(2). Steady-state kinetics indicate that amine-reduced CuAGAO is reoxidized by O(2) >10(3) times faster than the CoAGAO analogue. Complementary spectroscopic studies reveal that the difference in the second order rate constant, k(cat)/K(M)(O(2)), arises from the more negative redox potential of Co(III/II) in relation to Cu(II/I). Indistinguishable competitive oxygen-18 kinetic isotope effects are observed for the two enzymes and modeled computationally using a calibrated density functional theory method. The results are consistent with a mechanism where an end-on (η(1))-metal bound superoxide is reduced to an η(1)-hydroperoxide in the rate-limiting step.
分析了球形节杆菌铜胺氧化酶（AGAO）与钴取代蛋白的关系，其 O(2)还原机制。该酶利用酪氨酸衍生的托哌醌辅因子氧化伯胺并将 O(2)还原为 H(2)O(2)。稳态动力学表明，胺还原的 CuAGAO 被 O(2)再氧化的速率比 CoAGAO 类似物快 >10(3)倍。互补的光谱研究表明，二级反应速率常数 k(cat)/K(M)(O(2))的差异源于 Co(III/II)相对于 Cu(II/I)的更负氧化还原电位。两种酶的竞争氧-18 动力学同位素效应相似，并使用校准的密度泛函理论方法进行了计算模拟。结果与限速步骤中末端（η(1)）-金属结合的超氧化物还原为 η(1)-过氧化物的机制一致。
