Carbon Monoxide Metabolism in Roadside Soils

Air-dried soils which were equilibrated under relative humidities greater than 93% or moistened with liquid water showed marked increases in their capacities to oxidize CO to CO₂. Liquid water addition in excess of saturation resulted in lower CO oxidation rates, reflecting the limited diffusion of CO through the aqueous phase. After 35 days' storage under 100% relative humidity, the capacity for CO oxidation decreased to 21% of the value observed with a freshly collected sample. Incubation of this stored soil under an atmosphere containing 200 ppm of CO (250 mg/m³) for 21 days resulted in a sevenfold increase in CO oxidation. A correlation was noted between the CO oxidative activity and the history of previous exposure of soils to high ambient levels of CO. The organisms responsible for CO oxidation apparently comprise a small fraction of the microbial population in the soils. With a roadside soil the oxidation of CO provided the driving force for the assimilation of CO₂. The stoichiometry of the oxidative and assimilatory reactions in soil was in the range of values reported from laboratory studies with CO chemoautotrophs (carboxydobacteria). It is proposed that the population and activity of CO-oxidizing microorganisms increase in response to increasing levels of CO in the environment.     

一氧化碳的信号转导机制

很早 ,人们就注意到在人体的正常生理状况下有内源性一氧化碳 (ｃａｒｂｏｎｍｏｎｏｘｉｄｅ ,ＣＯ)的存在。近年来随着对一氧化氮 (ｎｉｔｒｉｃｏｘｉｄｅ ,ＮＯ)研究的深入和全面 ,另一类血管内皮舒张因子 (ｅｎｄｏｔｈｅｌｉｕｍ ｄｅｒｉｖｅｄｒｅｌａｘｉｎｇｆａｃｔｏｒ,ＥＤＲＦ)ＣＯ被认识 ,且实验表明 ,它还是重要的信使分子[1] 。实际上 ,ＣＯ从呼吸系统、心血管系统到神经系统、免疫系统均发挥调节作用。1 .ＣＯ信号的基本转导通路1 .1　ｃＧＭＰ途径　　ＣＯ在生物体内主要通过激活可溶性鸟苷酸环化酶 (ｓＧＣ)升高ｃＧＭ…     

Carbon Monoxide Oxidation by Methanogenic Bacteria

Different species of methanogenic bacteria growing on CO(2) and H(2) were shown to remove CO added to the gas phase. Rates up to 0.2 mumol of CO depleted/min per 10 ml of culture containing approximately 7 mg of cells (wet weight) were observed. Methanobacterium thermoautotrophicum was selected for further study based on its ability to grow rapidly on a completely mineral medium. This species used CO as the sole energy source by disproportionating CO to CO(2) and CH(4) according to the following equation: 4CO + 2H(2)O --> 1CH(4) + 3CO(2). However, growth was slight, and the growth rate on CO was only 1% of that observed on H(2)/CO(2). Growth only occurred with CO concentrations in the gas phase of lower than 50%. Growth on CO agrees with the finding that cell-free extracts of M. thermoautotrophicum contained both an active factor 420 (F(420))-dependent hydrogenase (7.7 mumol/min per mg of protein at 35 degrees C) and a CO-dehydrogenating enzyme (0.2 mumol/min per mg of protein at 35 degrees C) that catalyzed the reduction of F(420) with CO. The properties of the CO-dehydrogenating enzyme are described. In addition to F(420), viologen dyes were effective electron acceptors for the enzyme. The apparent K(m) for CO was higher than 1 mM. The reaction rate increased with increasing pH and displayed an inflection point at pH 6.7. The temperature dependence of the reaction rate followed the Arrhenius equation with an activation energy (DeltaHdouble dagger) of 14.1 kcal/mol (59.0 kJ/mol). The CO dehydrogenase activity was reversibly inactivated by low concentrations of cyanide (2 muM) and was very sensitive to inactivation by oxygen. Carbon monoxide dehydrogenase of M. thermoautotrophicum exhibited several characteristic properties found for the enzyme of Clostridium pasteurianum but differed mainly in that the clostridial enzyme did not utilize F(420) as the electron acceptor.     

Reaction of Oxyhemoglobin with Carbon Monoxide

The reaction of oxyhemoglobin and carbon monoxide was studied kinetically at pH 7.8 in a variety of suspending media. The dielectric constant of the suspending media, as well as the viscosity (and hence the Fick diffusion coefficients), was varied with the use of glycine, glycerol, and sucrose. The results showed that the reaction was unaltered by the various additions to the media, provided that the pO₂ and the concentration of carbon monoxide were held constant. Since the concentration of oxygen varies from medium to medium at constant pO₂ while the pCO varies at constant concentration of carbon monoxide, the differences in the reactions with oxygen and carbon monoxide were emphasized. The lack of variation of the rate constants with changes in dielectric constant can be interpreted as indicating that electrostatic effects are unimportant in this reaction.