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Biochem Biophys Res Commun. 2005 May 6;330(2):565-70.

Quinone reduction by Rhodothermus marinus succinate:menaquinone oxidoreductase is not stimulated by the membrane potential.

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Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, Apartado 127, 2784-505 Oeiras, Portugal.


Succinate:quinone oxidoreductase (SQR), a di-haem enzyme purified from Rhodothermus marinus, reveals an HQNO-sensitive succinate:quinone oxidoreductase activity with several menaquinone analogues as electron acceptors that decreases with lowering the redox midpoint potential of the quinones. A turnover with the low-potential 2,3-dimethyl-1,4-naphthoquinone that is the closest analogue of menaquinone, although low, can be detected in liposome-reconstituted SQR. Reduction of the quinone is not stimulated by an imposed K+-diffusion membrane potential of a physiological sign (positive inside the vesicles). Nor does the imposed membrane potential increase the reduction level of the haems in R. marinus SQR poised with the succinate/fumarate redox couple. The data do not support a widely discussed hypothesis on the electrogenic transmembrane electron transfer from succinate to menaquinone catalysed by di-haem SQRs. The role of the membrane potential in regulation of the SQR activity is discussed.

[Indexed for MEDLINE]

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