Kalimuthu Palraj, Kappler Ulrike, Bernhardt Paul V
School of Chemistry and Molecular Biosciences, University of Queensland , Brisbane, 4072, Australia.
J Phys Chem B. 2014 Jun 26;118(25):7091-9. doi: 10.1021/jp503963z. Epub 2014 Jun 16.
Sulfite dehydrogenase from the soil bacterium Sinorhizobium meliloti (SorT) is a periplasmic, homodimeric molybdoenzyme with a molecular mass of 78 kDa. It differs from most other well studied sulfite oxidizing enzymes, as it bears no heme cofactor. SorT does not readily reduce ferrous horse heart cytochrome c which is the preferred electron acceptor for vertebrate sulfite oxidases. In the present study, ferrocene methanol (FM) (in its oxidized ferrocenium form) was utilized as an artificial electron acceptor for the catalytic SorT sulfite oxidation reaction. Cyclic voltammetry of FM was used to generate the active form of the mediator at the electrode surface. The FM-mediated catalytic sulfite oxidation by SorT was investigated by two different voltammetric methods, namely, (i) SorT freely diffusing in solution and (ii) SorT confined to a thin layer at the electrode surface by a semipermeable dialysis membrane. A single set of rate and equilibrium constants was used to simulate the catalytic voltammograms performed under different sweep rates and with various concentrations of sulfite and FM which provides new insights into the kinetics of the SorT catalytic mechanism. Further, we were able to model the role of the dialysis membrane in the kinetics of the overall catalytic system.
来自土壤细菌苜蓿中华根瘤菌的亚硫酸盐脱氢酶（SorT）是一种周质同型二聚体钼酶，分子量为78 kDa。它与大多数其他经过充分研究的亚硫酸盐氧化酶不同，因为它不含血红素辅因子。SorT不容易还原亚铁马心血红蛋白c，而亚铁马心血红蛋白c是脊椎动物亚硫酸盐氧化酶的首选电子受体。在本研究中，二茂铁甲醇（FM）（以其氧化的二茂铁鎓形式）被用作SorT催化亚硫酸盐氧化反应的人工电子受体。FM的循环伏安法用于在电极表面生成介体的活性形式。通过两种不同的伏安法研究了FM介导的SorT催化亚硫酸盐氧化，即（i）SorT在溶液中自由扩散和（ii）SorT通过半透性透析膜限制在电极表面的薄层中。使用一组速率和平衡常数来模拟在不同扫描速率以及不同亚硫酸盐和FM浓度下进行的催化伏安图，这为SorT催化机制的动力学提供了新的见解。此外，我们能够模拟透析膜在整个催化系统动力学中的作用。
