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Deletion of COQ10 in Saccharomyces cerevisiae elicits a respiratory defect characterized by the absence of cytochrome c reduction, which is correctable by the addition of exogenous diffusible coenzyme Q2. Unlike other coq mutants with hampered coenzyme Q6 (Q6) synthesis, coq10 mutants have near wild-type concentrations of Q6. In the present study, we used Q-cycle inhibitors of the coenzyme QH2-cytochrome c reductase complex to assess the electron transfer properties of coq10 cells. Our results show that coq10 mutants respond to antimycin A, indicating an active Q-cycle in these mutants, even though they are unable to transport electrons through cytochrome c and are not responsive to myxothiazol. EPR spectroscopic analysis also suggests that wild-type and coq10 mitochondria accumulate similar amounts of Q6 semiquinone, despite a lower steady-state level of coenzyme QH2-cytochrome c reductase complex in the coq10 cells. Confirming the reduced respiratory chain state in coq10 cells, we found that the expression of the Aspergillus fumigatus alternative oxidase in these cells leads to a decrease in antimycin-dependent H2O2 release and improves their respiratory growth. [ABSTRACT FROM AUTHOR]

The unequivocal demonstration that the carbonate radical (CO3 •-) is produced from the reaction between the ubiquitous carbon dioxide and peroxynitrite, renewed the interest in the pathogenic roles of oxidants derived from the main physiological buffer, the bicarbonate-carbon dioxide pair. Here, we review the biochemical properties of both the carbonate radical and peroxymonocarbonate (HCO4 -), and discuss the evidence of their formation under physiological conditions. Overall, the review emphasizes the recognition of the biological relevance of oxidants derived from the main physiological buffer as a crucial step into the understanding and control of numerous pathological states. IUBMB Life, 59: 1 - 8, 2007 IUBMB Life, 59: 255-262, 2007 [ABSTRACT FROM AUTHOR]

Abstract: The origin of nitric oxide ( NO) in plants is unclear and an NO synthase (NOS)-like enzyme and nitrate reductase (NR) are claimed as potential sources. Here we used wild-type and NR-defective double mutant plants to investigate NO production in Arabidopsis thaliana in response to Pseudomonas syringae pv maculicola. NOS activity increased substantially in leaves inoculated with P. syringae. However, electron paramagnetic resonance experiments showed a much higher NO formation that was dependent on nitrite and mitochondrial electron transport rather than on arginine or nitrate. Overall, these results indicate that NOS, NR and a mitochondrial-dependent nitrite-reducing activity cooperate to produce NO during A. thaliana–P. syringae interaction. [Copyright &y& Elsevier]

Methionine sulfoxide is a post-translational protein modification that has been receiving increasing attention in the literature. Here we used electron paramagnetic resonance spin trapping techniques to show that free and peptide-bound methionine sulfoxide is oxidized by hydrogen peroxide/iron(II)-EDTA and peroxynitrite through the intermediacy of the hydroxyl radical to produce both ⋅CH3 and ⋅CH2CH2CH radicals. The results indicate that methionine sulfoxide residues are important targets of reactive oxygen- and nitrogen-derived species in proteins. Since the produced protein-derived radicals can propagate oxidative damage, the results add a new antioxidant route for the action of the enzyme peptide methionine sulfoxide reductase. [Copyright &y& Elsevier]