Bott M, Eikmanns B, Thauer R K
Eur J Biochem. 1986 Sep 1;159(2):393-8. doi: 10.1111/j.1432-1033.1986.tb09881.x.
Cell suspensions of Methanosarcina barkeri, grown on acetate, catalyzed the conversion of carbon monoxide and H2O to CO2 and H2 in stoichiometric amounts when methane formation was inhibited by bromoethanesulfonate. The specific activity was 80-120 nmol min-1 mg protein-1 at 5% CO in the gas phase. CO oxidation was coupled with the phosphorylation of ADP as indicated by a rapid increase of the intracellular ATP level upon start of the reaction. At least 0.1 mol ATP was formed/mol CO consumed. The onset of CO oxidation was also accompanied by an increase of the proton motive force (delta p) from 100 mV to 150 mV (inside negative). Addition of the uncoupler tetrachlorosalicylanilide to CO-metabolizing cells led to a rapid decrease of the ATP level and of delta p, and to an increase of the CO oxidation rate up to 70%. In the presence of the proton-translocating ATPase inhibitor N,N'-dicyclohexylcarbodiimide the phosphorylation of ADP was inhibited and CO oxidation slowed down, whereas delta p was almost unaffected. Inhibition of CO oxidation under these conditions was relieved by the addition of the protonophore tetrachlorosalicylanilide. The results indicate that in acetate-grown M. barkeri the free-energy change associated with the formation of CO2 and H2 from CO and H2O (delta G degrees = -20 kJ/mol) can be used to drive the phosphorylation of ADP and that the coupling proceeds via a chemiosmotic mechanism. A possible role of the carbon monoxide oxidation reaction as an energy-conserving site in acetate fermentation to CH4 and CO2 is discussed.
以乙酸盐为生长底物的巴氏甲烷八叠球菌细胞悬液，当用溴乙烷磺酸盐抑制甲烷生成时，能催化一氧化碳和水按化学计量比转化为二氧化碳和氢气。在气相中一氧化碳含量为5%时，比活性为80 - 120 nmol min⁻¹ mg蛋白质⁻¹。如反应开始时细胞内ATP水平迅速升高所示，一氧化碳氧化与ADP磷酸化相偶联。每消耗1摩尔一氧化碳至少形成0.1摩尔ATP。一氧化碳氧化开始时，质子动力势（Δp）也从100 mV增加到150 mV（内侧为负）。向代谢一氧化碳的细胞中添加解偶联剂四氯水杨酸苯胺会导致ATP水平和Δp迅速下降，并使一氧化碳氧化速率提高至70%。在存在质子转运ATP酶抑制剂N，N'-二环己基碳二亚胺的情况下，ADP磷酸化受到抑制，一氧化碳氧化减慢，而Δp几乎不受影响。在这些条件下，添加质子载体四氯水杨酸苯胺可缓解一氧化碳氧化的抑制。结果表明，在以乙酸盐生长的巴氏甲烷八叠球菌中，与一氧化碳和水形成二氧化碳和氢气相关的自由能变化（ΔG° = -20 kJ/mol）可用于驱动ADP磷酸化，且这种偶联通过化学渗透机制进行。讨论了一氧化碳氧化反应在乙酸盐发酵生成甲烷和二氧化碳过程中作为能量保存位点的可能作用。
