The impact of membrane-targeted cations on energy conversion
in membrane vesicles from Rb. capsulatus
M.A. Kozloval, A.Y. Mulkidjanian2,3
1Institute of Mitoengineering, Moscow State University, Moscow 119899, Russia
2Division of Biophysics, Faculty of Biology/Chemistry, University of Osnabrück, D-49069 Osnabrück, Germany
3A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia.
We have studied the impact of mitochondrially targeted penetrating cations on energy
conversion in membrane vesicles from phototrophic bacteria Rb. capsulatus
(chromatophores). The energy-converting enzymes of purple bacteria are closely related
to their mitochondrial counterparts, but can be synchronized by short flashes of light.
The same membranes contain electrochromic pigments, mostly carotenoids, which can
serve as internal voltmeters.
The mitochondrially targeted cations, did not affect notably the flash-triggered generation
of membrane potential (at least when added at < 1 μM), but accelerated its decay.
The similar uncoupling efficiency of SkQ1, MitoQ and C12TPP indicates the involvement
of the TPP moiety in the proton translocation. This uncoupling action could be partly
prevented by depletion of chromatophore preparation from fatty acids (via pre-washing
with bovine serum albumin, BSA). Addition of palmitic acid to the BSA-treated
chromatophores partially reversed the effect of BSA. We consider these data as an
evidence for the transmembrane, H+-conducting fatty acid cycling mediated by
penetrating cations, as suggested by Skulachev and co-workers (Severin et al. 2010).
Neither SkQ nor MitoQ affected the flash induced redox-changes of cytochrome b
in the cytochrome bc1 complex. Accordingly, these cations which,
most likely, can interact only with the quinone-reducing center N of the complex
(Gu et al., 2000), did not block the electron flow out of this center.
When added in concentration of > 5μM over antimycin A, SkQ1 could serve as an
electron shuttle, overcoming the antimycin block. This observation explains why the
addition of SkQ1 over antimycin induces a ROS burst in mitochondria.
The studies of the Zn-treated chromatophores, where the oxidation of cytochrome b
was retarded (Skulachev et al., 1967, Klishin et al. 2002, Mulkidjanian, 2007) have
shown that MitoQ and SkQ, when addded at > 1 μM slightly slowed down the reduction
of heme bh. Any slowing of this reaction, however, should be
accompanied by an increase in the ROS production.
We suggest that at high concentrations MitoQ and SkQ can bind to the cytochrome bc1
complex and affect the mechanism of ubiquinol oxidation in center P. This effect
could account for the pro-oxidant action of the mitochondrially targeted cations.
References
Gu, L.Q., L. Yu, and C.A. Yu. 1990. Biochim. Biophys. Acta 1015:482-492.
Klishin, S.S., W. Junge, and A.Y. Mulkidjanian. 2002. Biochim. Biophys. Acta 1553:177-182.
Mulkidjanian, A.Y. 2007. Photochem. Photobiol. Sci. 6:19-34.
Severin FF, Severina II, Antonenko YN, Rokitskaya TI, Cherepanov DA, Mokhova EN,
Vyssokikh MY, Pustovidko AV, Markova OV, Yaguzhinsky LS, Korshunova GA,
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Skulachev VP, Chistyakov VV, Jasaitis AA, Smirnova EG. 1967. Biochem.
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Homo Sapiens Liberatus Workshop, Moscow State University, May 2010