title: Quinone reduction by Rhodothermus marinus succinate:menaquinone oxidoreductase is not stimulated by the membrane potential.
abstract: 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.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, Apartado 127, 2784-505 Oeiras, Portugal.
authors.forename: Andreia S
authors.initials: AS
authors.lastname: Fernandes
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Konstantinov
authors.forename: Miguel
authors.initials: M
authors.lastname: Teixeira
authors.forename: Manuela M
authors.initials: MM
authors.lastname: Pereira
mesh_terms: D016227:Benzoquinones / Q000378:metabolism*; D008081:Liposomes; D008564:Membrane Potentials; D045245:Rhodothermus / Q000201:enzymology*; D013385:Succinate Dehydrogenase / Q000378:metabolism*
chemical_list: D016227:Benzoquinones; D008081:Liposomes; C004532:quinone; D013385:Succinate Dehydrogenase