The Role of Iron‐Sulfur Center 2 in Electron Transport and Energy Conservation in the NADH‐Ubiquinone Segment of the Respiratory Chain in Paracoccus denitrificans

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Abstract
The EPR spectra at 15.degree. K of reduced membrane particles of P. denitrificans exhibit resonance signals with g values, line shapes and temperature profile which are similar to the signals of the Fe-S centers observed in the NADH-ubiquinone segment of mitochondrial respiratory chains. These Fe-S centers are reducible with NADH, NADPH and chemically with dithionite. Sulfate-limited growth of P. denitrificans results in the loss of an EPR signal (gz .apprxeq. 2.05, gy .apprxeq. gx .apprxeq. 1.92) which has properties similar to those of Fe-S center 2 of the NADH dehydrogenase of mitochondrial origin [Candida utilis]. The loss of this signal is accompanied by a decrease in the NADH oxidase and NADH ferricyanide oxidoreductase activities to 30 and 40%, respectively, of the values found for succinate-limited growth conditions. Respiration in membrane particles from sulfate-limited cells loses its sensitivity to rotenone. Since sulfate-limited growth of P. denitrificans induces loss of site I phosphorylation these observations suggest a close correlation between site I phosphorylation, rotenone-sensitivity and the presence of an EPR signal with gz .apprxeq. 2.05 and gy .apprxeq. gx .apprxeq. 1.92.

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