PubMed · 836163
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R J Clark. 1977. Carbon monoxide diffusing capacity.. https://pubmed.ncbi.nlm.nih.gov/836163/
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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.
Resonance Raman spectra are reported for the carbon monoxide (CO) adduct of catalase formed from the reaction of peracetic acid or hydrogen peroxide with the azide adduct of catalase in the presence of CO. The expected three normal vibrations of the FE-CO fragment are detected at 1,908,593 and 543 cm-1 for the nu(C-O), delta(Fe-C-O) and nu(Fe-CO), respectively. The expected coordination of the phenolate group in this adduct is confirmed by the enhancement of an internal vibration of phenolate, nu 19a at 1,515 cm-1, and an extraordinary intensity enhancement of the nu(Fe-CO) mode.
Purified red blood cell cytosol is able to activate 2-aminofluorene (2AF) to N-hydroxy-2-aminofluorene. Apparent kinetic parameters are determined with and without methylene blue. The latter, which maintains haemoglobin in the reduced form and stimulates NADPH production, increases the affinity of the enzyme for the 2AF. This activity is inhibited by carbon monoxide while cyanide is without effect. The involvement of a peroxidative reaction or a one-electron oxidative mechanism involving free radicals may be excluded.