title: The alternative complex III of Rhodothermus marinus and its structural and functional association with caa3 oxygen reductase.
abstract: An alternative complex III (ACIII) is a respiratory complex with quinol:electron acceptor oxidoreductase activity. It is the only example of an enzyme performing complex III function that does not belong to bc1 complex family. ACIII from Rhodothermus (R.) marinus was the first enzyme of this type to be isolated and characterized, and in this work we deepen its characterization. We addressed its interaction with quinol substrate and with the caa3 oxygen reductase, whose coding gene cluster follows that of the ACIII. There is at least, one quinone binding site present in R. marinus ACIII as observed by fluorescence quenching titration of HQNO, a quinone analogue inhibitor. Furthermore, electrophoretic and spectroscopic evidences, taken together with mass spectrometry revealed a structural association between ACIII and caa3 oxygen reductase. The association was also shown to be functional, since quinol:oxygen oxidoreductase activity was observed when the two isolated complexes were put together. This work is thus a step forward in the recognition of the structural and functional diversities of prokaryotic respiratory chains.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, EAN, 2780-157 Oeiras, Portugal.
authors.forename: Patrícia N
authors.initials: PN
authors.lastname: Refojo
authors.forename: Miguel
authors.initials: M
authors.lastname: Teixeira
authors.forename: Manuela M
authors.initials: MM
authors.lastname: Pereira
mesh_terms: D003574:Cytochrome c Group / Q000737:chemistry* / Q000502:physiology; D045264:Cytochromes a / Q000737:chemistry* / Q000502:physiology; D045266:Cytochromes a3 / Q000737:chemistry* / Q000502:physiology; D014450:Electron Transport Complex III / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D005453:Fluorescence; D005810:Multigene Family; D045245:Rhodothermus / Q000378:metabolism*; D014812:Vitamin K / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D003574:Cytochrome c Group; D045266:Cytochromes a3; C435384:cytochrome caa(3); D014812:Vitamin K; D045264:Cytochromes a; D014450:Electron Transport Complex III; C023885:menadiol