M M Pereira

..The results presented here for these A-type enzymes are compared with those previously obtained for representative members of the B and C families...

..As the families of haem-copper oxidases can also be identified by their subunit II, a parallel evolution of subunits I and II is suggested...

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..In this report, we establish undoubtedly the existence of an alternative complex III, a functional substitute of the bc(1) complex, by its identification at both the biochemical and genomic level...

..With this testable hypothesis we intend to challenge the discussion and drive further experimentation to unravel the functional mechanism of SQRs and QFRs...

..The data are discussed in the framework of the evolution of oxidases within the superfamily of heme-copper oxidases...

..Overall, the results strongly suggest that Glu(498) plays a key role in the protonation events that occur at the trinuclear centre and in its stabilization, controlling therefore the binding of dioxygen and its further reduction...

..Comparison with the mitochondrial like oxygen reductase from Rhodobacter sphaeroides suggests that proton transfer from a strategically situated donor to the active site is a crucial step in the reaction mechanism of oxygen reductases...

..7. This behavior is consistent with the proposal that in these enzymes menaquinone reduction occurs close to heme bL, near to the periplasmic side of the membrane, and involving dissipation of the proton transmembrane gradient...

..This work is thus a step forward in the recognition of the structural and functional diversities of prokaryotic respiratory chains...

..4, the order is reversed: 246 mV for heme B and 199 mV for heme A3. The existence of redox anticooperativity was established by introducing a redox interaction parameter in a model of pairwise interacting redox centers...

..Both haems, B and A, present two transitions, have unusually low reduction potentials of -65 mV and an interaction potential of -52.5 mV...

..Finally, the possible contribution of these enzymes to the formation/dissipation of a transmembrane proton gradient is discussed, considering recent experimental and structural data...

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..Based on a thorough structural and amino acid sequence comparison, we propose R. marinus cytochrome c as the first characterized member of a new class of C-type cytochromes...

..Two (Tyr262(I) and Lys336(I), caa(3) numbering) out of three protonatable K-channel residues are proton active and redox sensitive in both proteins...

..400 mV. The determination of reduction potentials of the individual hemes c reported in this work provides the basis for further exploring the mechanism of electroprotonic energy transduction of this complex enzyme...

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..The redox potentials of the L386A and I494A mutants are shifted downwards by approx. 60 and 100 mV respectively. These changes correlate well with decreased catalytic efficiency of both mutants compared with the wild-type...

..The diversity of channels in haem-copper oxygen reductases exemplifies the plasticity of proton pathways that occurred throughout evolution, and strongly suggests a substantial role for water as the main proton carrier...

..0 M GuHCl (pH 7.0, 20 degrees C). The iron-sulfur cluster degrades upon polypeptide unfolding, resulting in an irreversible denaturation process...

..McoA probably contributes to copper and iron homeostasis in A. aeolicus...

..Biophys. Acta 1505 (2001) 185], and allow to identify the minimal essential elements for these enzymes...

..Rather, the extensive genomic analyses indicate that the differences concerning the several complexes are related to the organism phylogeny, i.e., to evolution and lateral gene transfer events...

..These results suggest that the membrane potential may play an active role in the regulation of the enzymatic activity of QO...

..Moreover, the open-reading-frames of the putative NhaD and PCD were shown to be co-transcribed with the other complex I genes encoded by nqoB. The possible role of these two genes in R. marinus complex I is discussed...

..The role of the membrane potential in regulation of the SQR activity is discussed...

..Remarkably, the coat-associated or the purified enzyme showed a half-life of inactivation at 80 degrees C of about 4 and 2 h, respectively, indicating that CotA is intrinsically highly thermostable...

..Based on these findings, we propose that the A. ambivalens cytochrome ba complex is analogous to the bc(1) complexes of bacteria and mitochondria, however with distinct subunits and heme types...

..EPR and resonance Raman data indicate that, presumably, folding in the presence of copper is indispensable for the correct structure of the trinuclear copper-containing site...

..5...

..At least five iron-sulfur centers are observed by EPR spectroscopy: two [2Fe-2S](2+/1+) and three [4Fe-4S](2+/1+) centers. By fluorescence spectroscopy a still unidentified chromophore was detected in R. marinus complex I...

..Although DLDH is generally part of the alpha-ketoacid dehydrogenase complexes in Bacteria and Eukarya, none of these complexes has yet been isolated from Sulfolobales. The metabolic role of DLDH in these organisms is discussed...

..The possible implications of this observation in the catalytic mechanism for sulfide oxidation are discussed, and the role of SQR in the sulfur dependent bioenergetics of A. ambivalens, linked to oxygen reduction, is addressed...

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..The implications of such conformational changes are discussed in relation to general redox-coupled proton pumping mechanisms in the heme-copper oxygen reductases...