Acetyl-CoA synthase, ACS

In contrast to the abundance of Fe-proteins, there are only six known nickel-containing enzymes hydrogenase, CO dehydrogenase (CODA), acetyl-CoA synthase (ACS), superoxide dismutase, urease, and S-methyl-CoM methylreductase. Among these enzymes, it exists in very diverse environments, including a dinickel site (urease), a Ni-Fe heterobinuclear site (hydrogenase), a Ni-Fe4S4 heterometallic... 

The nickel enzymes covered in this article can be divided into two groups redox enzymes and hydrolases. The five Ni redox enzymes are hydrogenase, CO dehydrogenase (CODH), acetyl-CoA synthase (ACS), methyl-Coenzyme M reductase (MCR), and superoxide dismutase (SOD). Glyoxalase-I and urease are Ni hydrolases. Ni proteins that are not enzymes are not covered, because they have been recently reviewed. These include regulatory proteins (NikR) and chaperonins and metal uptake proteins (CooJ, CooE, UreE, and ABC transporters). A recent crystal structure of NikR, shown in Figure l(i), is a notable recent achievement in this area. ... 

Three of the eight Ni enzymes, hydrogenase, CO dehydrogenase (CODH), and acetyl-CoA synthase (ACS), are Ni—Fe—S proteins. Hydrogenases play an important role in microbial energy metabolism by catalysing the reversible oxidation of hydrogen ... 

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... 

Also known as beta-alanine because of its similarity to the canonical amino acid L-lysine, it has been overproduced in E. coli. A strain was prepared, which included an aspartate decarboxylase gene panD) from C. glutamicum, overexpression of aspartase (aspA) and phosphoenolpyruvate carboxylase (ppc), and acetyl-CoA synthase (acs) and it resulted in total titers of 32 g 1 after 39 h from rich media supplemented by glucose and ammonium sulfate [61]. 

Acetyl-CoA synthase (ACS)/carbon monoxide dehydrogenase (CODH) is a multifunctional enzyme that catalyzes the interconversion of CO and CO2 (CODH... 

Central to acetogenesis [94], acetyl CoA synthase (ACS) effectively catalyzes the formation of acetyl CoA from CO and a cobalamin-like methyl carrier called the corrinoid iron sulfur protein (CoFeSP) (Eq. 12.8). 

In anaerobic environments, fhe biological redox-processing of carbon monoxide and carbon dioxide is accomplished by carbon monoxide dehydrogenases (CODH), which are often found in combination with a second enzyme, acetyl CoA synthase (ACS, see above) [124]. In the CODH/ACS bifunctional enzymes, the two substratebinding prosthetic groups, the A cluster (site of acetyl CoA synthesis and decarbonylation, see previous section) and the C cluster (site of CO/CO2 interconversion) are located in the a and P subunits, respectively. CODH from R. ruhrum is not associated with ACS. The CO produced at the C-cluster travels via a tunnel through the enzyme to the a subunit where it is processed by acetyl CoA synthase (the A-cluster) [125]. CODH catalyzes the interconversion of CO2 and CO (Eq. 12.11). 

Fig. 11. Active sites and reactions of the bifunctional CODH/ACS. For synthesis of acetyl-CoA, two electrons are transferred from external electron donors to Cluster B of the CODH subunit. Electrons are relayed to Cluster C which reduces CO2 to CO. The CO is proposed to be channeled to Cluster A of the ACS subunit to form a metal-CO adduct that combines with the methyl group of the CFeSP and CoA to form acetyl-CoA. For utilization of acetyl-CoA, these reactions are reversed. The abbreviations are CODH, CO dehydrogenase ACS, acetyl-CoA synthase CFeSP, the corrinoid iron-sulfur protein CoA, Coenzyme A.

Fig. 7. Enzyme-coupled assay in which the hydrolase-catalyzed reaction releases acetic acid. The latter is converted by acetyl-CoA synthetase (ACS) into acetyl-CoA in the presence of (ATP) and coenzyme A (CoA). Citrate synthase (CS) catalyzes the reaction between acetyl-CoA and oxaloacetate to give citrate. The oxaloacetate required for this reaction is formed from L-malate and NAD in the presence of L-malate dehydrogenase (l-MDH). Initial rates of acetic acid formation can thus be determined by the increase in adsorption at 340 nm due to the increase in NADH concentration. Use of optically pure (Ry- or (5)-acetates allows the determination of the apparent enantioselectivity i app i81)-...

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)). 

Scheme 1.18 Diagram of the Wood-Ljiungdahl pathway used in one-carbon metabolism of anaerobic organisms [167. CODH stands for carbon monoxide dehydrogenase and ACS for acetyl-CoA synthase (adapted from [134]).

The crystallographic restrlts, that support the existence of a gating mechanism for CO diffusion from the C-cluster, where it is synthesized, to the A-cluster, can be used to re-interpret several previously reported hypotheses. For instance, lindahl et al. proposed that the C and A-clusters, known to be magnetically isolated, were nevertheless coupled through conformational changes [184]. This can now be understood in terms of C-duster-synthesized CO accessibility to the A-duster. The proposed reductase (CO synthesis) and synthase (acetyl-CoA synthesis) modes for CODH/ACS were based on the observation that when the CO2 reduction was carried out in the absence of substrates for acetyl-CoA synthesis, CO production from CO2 and reductant had lower k j and higher than when those substrates... 

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