CO Dehydrogenase of Methanogens
CO dehydrogenase has a central role in the anaerobic component of the global carbon cycle. The anaerobic decomposition of complex organic matter involves microbial food chains (consortia) in which acetate is the most abundant intermediate. The acetate is primarily metabolized by acetotrophs, terminal organisms of the food chain, utilizing a pathway in which activated acetate (acetyl-CoA) is cleaved by CO dehydrogenase. The enzyme also catalyzes the synthesis of acetyl-CoA in the acetyl-CoA Ljungdahl-Wood pathway of homoacetogens (see Chapters 1 and 3). Although the physiology of these anaerobes are highly variable, the unity of biochemistry predicts that the underlying chemistry of their metabolism is basically the same. This principal of biochemistry is vividly evident in the CO dehydrogenase (acetyl-CoA cleaving) of acetotrohic methanogens from the Archaea domain; the enzyme has properties that are surprisingly similar to the CO dehydrogenase (acetyl-CoA synthesizing) of homoacetogens from the Bacteria domain. CO dehydrogenases also function in autotrophic methanogens to synthesize acetyl-CoA from CO2 in a process fundamentally similar to the Ljungdahl-Wood pathway. The extreme phylogenetic diversity between the two domains offer a unique opportunity for studies aimed at understanding the mechanism and evolution of CO dehydrogenases in anaerobes.
KeywordsMidpoint Potential Methanosarcina Barkeri Complex Organic Matter Carbon Monoxide Dehydrogenase Aceticlastic Methanogen
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