PubMed · 8538468
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M Perrella, I Denisov. 1995. Low-temperature electrophoresis methods.. https://doi.org/10.1016/0076-6879(95)59057-9
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Diverse microorganisms couple the oxidation of carbon monoxide gas (CO) to the reduction of protons, producing hydrogen gas (H2) using nickel-containing CO dehydrogenase/energy-converting hydrogenase (Ni-CODH/ECH). Although this process yields one of the lowest free-energy gains in biology, its physiological role at environmentally relevant CO levels remains unresolved. Here, we show that Ni-CODH/ECH functions as a survival-oriented energy conservation system that enables heterotrophic facultative anaerobes to survive electron acceptor limitation, rather than primarily supporting growth or CO detoxification. Analysis of 387 genomes of Anoxybacillaceae species revealed that Ni-CODH/ECH had a patchy distribution and, with one exception, was mutually exclusive with the oxygen-tolerant molybdenum-containing CODH, suggesting ecological specialization. Culture experiments using three isolates (Parageobacillus sp. G301, P. thermoglucosidasius NBRC 107763, and Thermolongibacillus altinsuensis B1-1) demonstrated that CO-dependent proton respiration is activated during stationary phase when exogenous electron acceptors are limiting, maintaining cell density under 25% CO, whereas no effect was observed in a Ni-CODH knockout (ΔcooCSF) strain. RNA-seq analysis of Parageobacillus sp. G301 under twelve conditions revealed that Ni-CODH/ECH genes are highly expressed (top 0.2%-1.9% of all genes) under electron acceptor-free conditions, independent of CO presence, under the predicted control of the redox-dependent transcriptional repressor Rex. ΔcooCSF cultures accumulated more CO than the wild-type (WT), suggesting trace CO scavenging by the WT. Together, our results redefine Ni-CODH/ECH as a redox-regulated auxiliary energy-conservation strategy that supports survival and maintenance in anaerobic energy-limited environments using two ubiquitous substrates. This work extends the carboxydovore paradigm of trace gas-based survival from aerobic to spatiotemporally variable anaerobic environments.
A highly selective ligand exchange reaction is realized in the self-assembled monolayer (SAM) of a triruthenium cluster on a gold electrode surface under precise electrochemical potential control. CO as well as NO molecules, which are known to play key roles in many chemical, biological, and environmental systems, can be efficiently introduced into the SAM by electrochemically tuning the electronic state of the Ru site. These unique surface reactions are more convenient and efficient than conventional ligand exchange reactions in solution and could be used for the elucidation of the electron-transfer mechanism in a biological system as well as in the development of molecular sensors and devices.
The equilibria of oxygen binding to and kinetics of CO combination with the symmetrical iron-zinc hybrids of a series of variants of human adult hemoglobin A have been measured at pH 7 in the presence of inositol hexaphosphate (IHP). In addition, the kinetics of CO combination have also been measured in the absence of IHP. The hybrids have the heme groups of either the alpha or the beta subunits replaced by zinc protoporphyrin IX, which is unable to bind a ligand and is a good model for permanently deoxygenated heme. The variants examined involve residues located in the alpha1beta2 interface of the hemoglobin tetramer. Alterations of residues located in the hinge region of the interface are found to affect the properties of both the alpha and the beta subunits of the protein. In contrast, alterations of residues in the switch region of the interface have substantial effects only on the mutant subunit and are poorly communicated to the normal partner subunit. When the logarithms of the rate constants for the combination of the first CO molecule with a single subunit in the presence of IHP are analyzed as functions of the logarithms of the dissociation equilibrium constants for the binding of the first oxygen under the same conditions, a linear relationship is found. The relationship is somewhat different for the alpha and beta subunits, consistent with the well-known differences in the geometries of their ligand binding sites.