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Studies on the Physiological Electron Donor for Cytochrome C Oxidase in Nitrobacter winogradskyi

Author(s): Tanzima Yeasmin | Yoshihiro Fukumori

Journal: Journal of Biological Sciences
ISSN 1727-3048

Volume: 1;
Issue: 9;
Start page: 846;
Date: 2001;
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Keywords: Cytochromes | respiratory chain | electron donor | Nirrobactr winogradskyi

Terminal respiratory system of an autotrophic nitrite- oxidizing bacterium, Nitrobacter winogradskyi was reconstructed with the purified components in vitro. Cytochrome aa3-type cytochrome c oxidase, soluble cytochrome c oxidase, soluble cytochrome c-550 and membrane-bound c-551 were purified from the bacterium to electrophoretically homogeneous states, respectively. Oxidation�s of the soluble ferro-cytochrome c-550 and membrane�bound ferrocytochrome c-551 by the cytochrome c oxidase was kinetically analyzed. Value of affinity constant (Km) and maximum velocity (Vmax) for the soluble cytochrome c-550 were 5.78 μ M and 251.5 sec-1 respectively, while values of Km and Vmax for the membrane�bound cytochrome c-551 were 3.2 μM and 88.7 sec-1respectively. The oxidation of membrane�bound ferro-cytochrome c-551 with the cytochrome c oxidase was accelerated by the addition of soluble cytochrome c-550, while oxidation of soluble cytochrome c-550 with enzyme was inhibited by the addition of membrane bound cytochrome c-551. Although membrane-bound cytochrome c-551 could be electron donor for cytochrome c oxidase, the soluble cytochrome c�550 seems to function as electron mediator between membrane bound cytochrome c-551 and cytochrome c oxidase in vivo.
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