Yeast cytochrome c oxidase: a model system to study mitochondrial forms of the haem-copper oxidase superfamily.

The known subunits of yeast mitochondrial cytochrome c oxidase are reviewed. The structures of all eleven of its subunits are explored by building homology models based on the published structures of the homologous bovine subunits and similarities and differences are highlighted, particularly of the core functional subunit I. Yeast genetic techniques to enable introduction of mutations into the three core mitochondrially-encoded subunits are reviewed

Enhanced co-tolerance and co-sensitivity from long-term metal exposures of heterotrophic and autotrophic components of fluvial biofilms

Understanding the interactive effects of multiple stressors on ecosystems has started to become a major concern. The aim of our study was therefore to evaluate the consequences of a long-term exposure to environmental concentrations of Cu, Zn and As on the pollution induced community tolerance (PICT) of lotic biofilm communities in artificial indoor channels. Moreover, the specificity of the PICT was assessed by evaluating the positive and negative co-tolerance between these metals. Photosynthetic efficiency and substrate-induced respiration (SIR), targeting the autotrophic and heterotrophic communities respectively were used in short-term inhibition bioassays with Cu, Zn and As to assess sensitivities of preexposed biofilms to the metals tested. Diversity profiles of a phototrophic, eukaryotic and prokaryotic community in biofilms following the different treatments were determined and analyzed with principal component analysis. The results demonstrated that pre-exposure to metals induced structural shifts in the community and led to tolerance enhancements in the phototrophic and heterotrophic communities. On the other hand, whatever the functional parameter used (i.e. photosynthesis and SIR), communities exposed to Cu were more tolerant to Zn and vice versa. Furthermore, only phototrophic communities pre-exposed to As developed tolerance to Cu but not to Zn, whereas no co-tolerance between Cu and As was observed in the heterotrophic communities. Finally, phototrophic and heterotrophic communities exposed to Cu and Zn became more sensitive to As, reflecting a negative co tolerance between these metals. Overall, our findings support the fact that although the mode of action of the different metals is an important driver for the structure and thus the tolerance of the communities, it appears that the detoxification modes are the most important factors for the occurrence of positive or negative co-tolerance

NO synthase isoforms specifically modify peroxynitrite reactivity

International audienceNitric oxide synthases (NOSs) are multi-domain hemothiolate proteins that are the sole source of nitric oxide (NO) in mammals. NOSs can also be a source or a sink for peroxynitrite (PN), an oxidant that is suspected to be involved in numerous physiopathological processes. In a previous study, we showed that the oxygenase domain of the inducible NOS (iNOSoxy) reacts with PN and changes its oxidative reactivity [Maréchal A, Mattioli TA, Stuehr DJ & Santolini J (2007) J Biol Chem 282, 14101-14112]. Here we report a similar analysis on two other NOS isoforms, neuronal NOS (nNOS) and a bacterial NOS-like protein (bsNOS). All NOSs accelerated PN decomposition, with accumulation of a similar heme intermediate. The kinetics of PN decomposition and heme transitions were comparable among NOSs. However, their effects on PN reactivity differ greatly. All isoforms suppressed PN two-electron oxidative activity, but iNOSoxy enhanced PN one-electron oxidation and nitration potencies, the oxygenase domain of nNOS (nNOSoxy) affected them minimally, and bsNOS abolished all PN reactivities. This led to the loss of both NOS and PN decomposition activities for nNOSoxy and iNOSoxy, which may be linked to the reported alterations in their electronic absorption spectra. Bacterial bsNOS was affected to a lesser extent by reaction with PN. We propose that these differences in PN reactivity among NOSs might arise from subtle differences in their heme pockets, and could reflect the physiological specificity of each NOS isoform, ranging from oxidative stress amplification (iNOS) to detoxification (bsNOS)