Electron-transport chain and coupled oxidative phosphorylation in methanol-grown Paracoccus denitrificans
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Methanol dehydrogenase of Paracoccus denitrificans was shown to be very similar to the enzyme of Pseudomonas sp, M. 27. The Km value for methanol with excess activator (ammonium ions) is 35 μM. The pH optimum for enzyme activity with 2,6-dichlorophe-nolindophenol as electronacceptor was at 9.0 A CO-binding type of cytochrome c was present only in cells grown with methanol as carbon and energy source.
It has been shown that methanol-oxidation involves electron-transport via cytochrome c and an a-type cytochrome to oxygen. Antimycin A did not inhibit this electron transport and 90% inhibition was obtained by 375 μM potassium cyanide. Electron transport from endogenous substrates is possible via cytochrome b and possibly cytochrome o to oxygen. Potassium cyanide inhibited 90% of the electron transport via this pathway at a concentration of 1.42 mM. Measurement of respiration-driven proton translocation proved that during oxidation of methanol to formaldehyde by oxygen one mole of adenosine triphosphate is synthesized in the site 3 region of the electron transport chain. The → H+/O value found confirmed the → H+/site ratio of 3–4 found in heterotrophic grown cells. During electron transport from endogenous substrates to oxygen there is a possible synthesis of 3 moles of adenosine triphosphate.
In heterotrophically grown cells electron transfer to oxygen follows almost only the branch of the respiratory chain containing cytochrome o. In methanol-grown cells the pathway via the a-type cytochrome seems more important.
Key wordsMethanol dehydrogenase Autotrophic growth Electron transport chain Oxidative phosphorylation Proton translocation Paracoccus denitrificans
electron paramagnetic resonance
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