Localization and mobility of coenzyme Q in lipid bilayers and membranes.
We have studied the mobility of coenzyme Q (CoQ) in lipid bilayers and mitochondrial membranes in relation to the control of electron transfer activities. A molecular dynamics computer simulation in the vacuum yielded a folded structure for CoQ10, with a length of only 21 A. Using this information we were able to calculate diffusion coefficients in the range of 10(-6) cm2/s in good agreement with those found experimentally by fluorescence quenching of pyrene derivatives. To investigate if CoQ diffusion may represent the rate-limiting step of electron transfer, we reconstituted complexes I and III and assayed the resulting NADH-cytochrome c reductase activity in presence of different CoQ10 levels and at different distances between complexes; the experimental turnovers were higher than the collision frequencies calculated using diffusion coefficients of 10(-9) cm2/s but compatible with values found by us by fluorescence quenching. Since the experimental turnovers are independent of the distance between complexes, we conclude that CoQ diffusion is not rate-limiting for electron transfer.
Dipartimento di Biochimica G. Moruzzi, Università di Bologna, Italy. lenaz@biocfarm.unibo.it
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Lenaz
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Fato
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Di Bernardo
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Jarreta
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Costa
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Genova
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Parenti Castelli
D000818:Animals; D003198:Computer Simulation; D004579:Electron Transport; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry*; D008928:Mitochondria / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008968:Molecular Conformation; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism*
D008051:Lipid Bilayers; D014451:Ubiquinone