β Scribed by H. W. Verseveld; A. H. Stouthamer
No coin nor oath required. For personal study only.
Methanol dehydrogenase of Paracoccus de-nitr~'cans 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 ~tM. The pH optimum for enzyme activity with 2,6-dichlorophenolindophenol as electronacceptor was at 9.0. A CObinding 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 cytochromec and an a-type cytochrome to oxygen. Antimycin A did not inhibit this electron transport and 90 % inhibition was obtained by 375~tM 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 1.42mM. 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 methanolgrown cells the pathway via the a-type cytochrome seems more important.
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