ELECTRON-SPIN RELAXATION OF IRON-SULFUR PROTEINS STUDIED BY MICROWAVE-POWER SATURATION
ELECTRON-SPIN RELAXATION OF IRON-SULFUR PROTEINS STUDIED BY MICROWAVE-POWER SATURATION
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DOI：
10.1016/0005-2795(78)90509-3
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发表时间：
1978-01-01
期刊：
影响因子：
--
通讯作者：
HALL, DO
中科院分区：
文献类型：
--
作者：
RUPP, H;CAMMACK, R;HALL, DO
The electron-spin relaxation of Fe-S centers in a range of simple proteins ([bovine adrenal, spinach, Spirulina maxima, Bacillus stearothermophilus, Zea mays, Medicago sativa, Chromatium, Halobacterium halobium and Clostridium pasteurianum] ferredoxin, high-potential Fe-S protein and rubredoxin [C. pasteurianum]) was investigated by means of the temperature dependence and microwave power saturation of the EPR signal. The proteins containing [2Fe-2S] centers all showed temperature optima higher than those for [4Fe-4S] centers, but the difference between the slowest-relaxing [4Fe-4S] protein (Chromatium high-potential Fe-S protein) and the fastest-relaxing [2Fe-2S] protein (Halobacterium halobium ferredoxin) was small. A greater distinction was seen in the power saturation behavior at low temperature (10-20 K). The behavior of the signal intensity as a function of microwave power was analyzed in terms of the power for half saturation P1/2 and the degree of homogeneous/inhomogeneous broadening. The effect of distorting the protein structure by salts, organic solvents and urea was to decrease the electron-spin relaxation rate as shown by a decreased value of P1/2. The addition of Ni2+ as a paramagnetic perturbing agent caused an increase in the electron-spin relaxation rate of all the the proteins, with the exception of adrenal ferredoxin, as shown by an increased P1/2 and, in a few cases, broadening of the linewidth. Ferricyanide, a commonly used oxidizing agent, has similar effects. These results are discussed in relation to the use of paramagnetic probes to determine whether Fe-S centers are near to a membrane surface. Spin-spin interactions between 2 paramagnetic centers in a protein molecule such as a 2[4Fe-4S] ferredoxin, lead to more rapid electron-spin relaxation. This method was used to detect a spin-spin interaction between molybdenum V and center Fe-SI in [bovine milk] xanthine oxidase.
