Acetyl-CoA Wood-Ljungdahl pathway

Drake HL. 1994. Acetogenesis, acetogenic bacteria, and the acetyl-CoA Wood/ Ljungdahl pathway past and current perspectives. In Drake HL, editor. Acetogenesis. New York Chapman Hall. 

Drake HL (1994) Acetogenesis, acetogenic bacteria, and the acetyl-CoA Wood/ Ljungdahl pathway past and current perspectives. In Drake HL (ed) Acetogenesis. Chapman and Hall, New York, pp 3-60 Dubos RJ (1988) Pasteur and modem science. Science Tech, Madison Ebner H (1985) Process for the production ofvinegar with more than 12g/100ml acetic acid. US Patent 4,503,078... 

The Reductive Acetyl-CoA Pathway (Wood-Ljungdahl Pathway)... 

Conceptually, the simplest way to synthesize an organic molecule is to construct it one carbon at a time (Ragsdale and Pierce, 2008). The Woods—Ljungdahl pathway (Figure 15.3) does just that, synthesising acetyl-CoA from CO2. Carbon monoxide dehydrogenase, CODH and acetyl-CoA synthase, ACS are responsible for the reduction of CO2 to CO and the subsequent formation of acetyl-CoA (Drennan et al., 2004). CODH/ACS... 

The bifunctional carbon monoxide dehydrogenase (CODH)/acetyl-CoA synthase enzyme is a key enzyme involved in the Wood-Ljungdahl pathway of carbon fixation that operates in anaerobic bacteria. As such, it is a major player in the global carbon cycle. The CODH component of the enzyme catalyzes the reversible reduction of CO2 to CO (Equation (15)), which is then channeled to the ACS active site where it reacts with CoA and a methyl group provided by the corrinoid iron-sulfur protein (CFeSP) to form acetyl-CoA 30 (Equation (16)). 

This acetyl-CoA pathway (or Wood-Ljungdahl pathway) involves reduction by H2 of one of the two molecules of CO2 to the methyl group of methyl-tetrahydromethanopterin in methanogens and of methyltetra-hydrofolate in acetogens. The pathway utilized by methanogens is illustrated in Fig. 15-22. ... 

Fermentation of hexose yields two pyruvates, and pyruvate is further oxidized to two acetyl CoA and two CO2 by the enzyme pyruvate ferredoxin oxidoreductase. Then, the two acetyd CoAs are converted to two acetates. The 4 moles ATP per hexose produced are used for further metabolism. The oxidation-reduction balance is achieved by reduction of both CO2 molecules to a third acetyl CoA and finally to acetate by the Wood-Ljungdahl pathway. The NADH and reduced ferredoxin generated from the oxidized forms during fermentation of hexose are the source of reducing power. One CO2 is reduced to 5-methyltetrahydrofolate. The first reaction in this pathway (reaction 4, O Fig. 1-4) is the formation of formate catalyzed by an unusual tungsten-selenoprotein formate dehydrogenase (Yamamoto et al. 1983). For C. thermoaceticum, the electron donor is NADPH. 

This is a noncyclic pathway that also results in the fixation of two molecules of C02 to form acetyl-CoA. It was elucidated by Wood, Ljungdahl, Thauer and others as a pathway which is used by acetogenic bacteria to synthesize acetate from C02 in their energy metabolism [21]. The acetyl-CoA pathway resembles the Monsanto process of acetate synthesis from CO and methanol, with one molecule of C02 being reduced to the level of methyltetrahydropterin, while another C02 molecule is reduced to the level of carbon monoxide in the reaction catalyzed by the nickel-dependent carbon monoxide dehydrogenase (Figure 3.3). 

The synthesis of acetyl-CoA by the Ljungdahl-Wood pathway of autotrophic carbon fixation in diverse bacteria and archaea is catalyzed by a Co- and Fe-containing corrinoid iron-sulfur protein (CoFeSP). This protein participates in the transfer of a methyl group from A -methyltetrahydrofolate to the cob(I)amide of CoFeSP to give a methylcob(III)amide, from which the methyl group is transferred to the reduced Ni-Ni-(4Fe-4S) active site cluster A of acetyl-CoA synthase (27). 

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