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J Biol Chem. 2012 Apr 20;287(17):14215-25. doi: 10.1074/jbc.M112.348813. Epub 2012 Mar 5.

Menaquinone-7 is specific cofactor in tetraheme quinol dehydrogenase CymA.

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  • 1Institute of Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.


Little is known about enzymatic quinone-quinol interconversions in the lipid membrane when compared with our knowledge of substrate transformations by globular enzymes. Here, the smallest example of a quinol dehydrogenase in nature, CymA, has been studied. CymA is a monotopic membrane tetraheme c-type cytochrome belonging to the NapC/NirT family and central to anaerobic respiration in Shewanella sp. Using protein-film electrochemistry, it is shown that vesicle-bound menaquinone-7 is not only a substrate for this enzyme but is also required as a cofactor when converting other quinones. Here, we propose that the high concentration of quinones in the membrane negates the evolutionary pressure to create a high affinity active site. However, the instability and reactivity of reaction intermediate, semiquinone, might require a cofactor that functions to minimize damaging side reactions.

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