Effect of solution viscosity on intramolecular electron transfer in sulfite oxidase
Effect of solution viscosity on intramolecular electron transfer in sulfite oxidase
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DOI：
10.1021/bi016059f
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发表时间：
2002-05-07
期刊：
影响因子：
2.9
通讯作者：
Enemark, JH
中科院分区：
文献类型：
--
作者：
Feng, CJ;Kedia, RV;Enemark, JH
我们以前的研究已经表明，鸡肝亚硫酸盐氧化酶的血红素和钼中心之间的分子内电子转移速率常数（JET）根据反应条件从大约20到1400 s（-1）变化[帕切科，A.，哈扎德J.T.，Tollin，G.，和Enemark，J. H.（1999）J.Biol.Inorg.Chem.4，390-401]。这两个中心是由一个灵活的多肽环连接，这表明构象的变化，改变钼-铁距离，可能会发挥重要作用，在所观察到的IET率。在本研究中，我们用激光闪光光解法研究了亚硫酸氧化酶的IET与溶液粘度的关系。通过加入聚乙二醇400或蔗糖，溶液粘度在1.0- 2.0cP范围内变化。在任一viscosogn的存在下，随着溶剂粘度的增加，观察到IET速率常数值的明显降低。IET速率常数与粘度的负0.7次方成线性关系。稳态动力学和EPR实验与以下解释一致，即粘度而不是所添加的增粘剂的其他性质是IET速率对溶剂组成的依赖性的原因，结果与亚硫酸盐氧化酶中构象变化对IET的作用一致，这有助于，为了澄清Mo和Fe中心之间的大IET速率常数与长距离之间的不一致性，（类似于32埃）在晶体结构中观察到的这两个金属中心之间[基斯克，C.，Schindelin，H.，帕切科，A.，Wehbi，W.，加内特河，巴西-地M.，拉贾戈帕兰角五、Enernark，J.H.，和Rees，D. C.（1997）Cell 91，973-983]。
Our previous studies have shown that the rate constant for intramolecular electron transfer JET) between the heme and molybdenum centers of chicken liver sulfite oxidase varies from similar to20 to 1400 s(-1) depending upon reaction conditions [Pacheco, A., Hazzard. J. T., Tollin, G., and Enemark, J. H. (1999) J. Biol. Inorg. Chem. 4, 390-401]. These two centers are linked by a flexible polypeptide loop, suggesting that conformational changes, which alter the Mo-Fe distance, may play an important role in the observed IET rates. In this study, we have investigated IET in sulfite oxidase using laser flash pliotolysis as a function of solution viscosity, The solution viscosity was varied over the range of 1.0-2.0 cP by addition of either polyethylene glycol 400 or sucrose. In the presence of either viscosogn, an appreciable decrease in the IET rate constant value is observed with an increase in the solvent viscosity. The IET rate constant exhibits a linear dependence on the negative 0.7th power of the viscosity. Steady-state kinetics and EPR experiments are consistent with the interpretation that viscosity, and not other properties of the added viscosogens, is responsible for the dependence of IET rates on the solvent composition, The results are consistent with the role of conformational changes on IET in sulfite oxidase, which help,, to clarify the inconsistency between the large rate constant for IET between the Mo and Fe centers and the long distance (similar to32 Angstrom) between these two metal centers observed in the crystal structure [Kisker, C., Schindelin, H., Pacheco, A., Wehbi, W., Garnett, R. M., Rajagopalan, K. V., Enernark, J. H., and Rees, D. C. (1997) Cell 91, 973-983].