Probing variable axial ligation in nickel superoxide dismutase utilizing metal lopeptide-based models: Insight into the superoxide disproportionation mechanism
Probing variable axial ligation in nickel superoxide dismutase utilizing metal lopeptide-based models: Insight into the superoxide disproportionation mechanism
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DOI：
10.1021/ja0731625
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发表时间：
2007-11-28
影响因子：
15
通讯作者：
Shearer, Jason
中科院分区：
文献类型：
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作者：
Neupane, Kosh P.;Gearty, Kristie;Shearer, Jason
镍超氧化物歧化酶(NiSOD)是一种细菌金属酶，具有单核Ni中心，通过在Ni-II和Ni-III氧化态之间循环来催化O2(中心点-)的歧化。在这里，我们用薄膜伏安法从几个SOD活性金属多肽模型([Ni((SODH)-H-M2(1)X)]；(SODH)-H-M2(1)X=H_2N-XCDLPCG-COOH；X=H，D，或A)中得到证据，在催化过程中，NiSOD的Ni中心很可能保持五配位。N-3-和CN-滴定研究表明，[Ni(SODM2H(1)X)]的O-2(中心点)歧化反应是通过外球机制进行的。计算得到的[Ni-II(SODM2)]/[Ni-III(SODM2)]自交换反应的核重组能与实验测定的k(O)值(类似于450 S(-1))表明，轴向配位通过优化Ni-II/Ni-III氧化还原对使其接近O-2(中心点)还原和氧化对的中点来增强[Ni(SODM2)](以此类推)中的O-2(中心点)歧化反应.
Nickel superoxide dismutase (NiSOD) is a bacterial metalloenzyme that possesses a mononuclear Ni-center and catalyzes the disproportionation Of O2(center dot-) by cycling between Ni-II and Ni-III oxidation states. Herein we present evidence from several SOD active metallopeptide maquettes ([Ni((SODH)-H-M2(1)X)]; (SODH)-H-M2(1)X = H2N-XCDLPCG-COOH; X = H, D, or A) that the Ni-center of NiSOD most likely remains five-coordinate during SOD catalysis using thin-film voltammetry. N-3- and CN- titration studies suggest that O-2(center dot-) disproportionation by [Ni(SODM2 H(1)X)] proceeds via an outersphere mechanism. Computationally derived values for the nuclear reorganization energy of the [Ni-II(SODM2)]/[Ni-III(SODM2)] self-exchange reaction combined with the experimentally determined value for k(o) (similar to 450 s(-1)) suggest that axial ligation enhances the O-2(center dot-) disproportionation reaction in [Ni(SODM2)] (and NiSOD by analogy) by optimizing the Ni-II/Ni-III redox couple such that it is close to the midpoint of the O-2(center dot-) reduction and oxidation couples.