Effect of solution viscosity on intramolecular electron transfer in sulfite oxidase

被引:107
作者
Feng, CJ
Kedia, RV
Hazzard, JT
Hurley, JK
Tollin, G [1 ]
Enemark, JH
机构
[1] Univ Arizona, Dept Biochem & Mol Biophys, Tucson, AZ 85721 USA
[2] Univ Arizona, Dept Chem, Tucson, AZ 85721 USA
关键词
D O I
10.1021/bi016059f
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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].
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页码:5816 / 5821
页数:6
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