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Distribution and Biological Functions of Pyruvate Carboxylase in Nature
Published in D. B. Keech, J. C. Wallace, Pyruvate Carboxylase, 2018
Under some circumstances, where interfering enzyme activities (e.g., lactate dehydrogenase,211 NADH oxidase, or acetyl-CoA hydrolase) are insignificant (e.g., after partial purification), more convenient coupled spectrophotometric assays have been used. However, since it is extremely rare for pyruvate carboxylase activity to be present in excess over lactate dehydrogenase or NADH oxidase in tissue homogenates, most workers have settled for the radiochemical assay in preference to the spectrophotometric assay employing malate dehydrogenase to couple NADH oxidation to oxaloacetate production.899
The role of short-chain fatty acids in the interplay between gut microbiota and diet in cardio-metabolic health
Published in Gut Microbes, 2021
Ana Nogal, Ana M. Valdes, Cristina Menni
Acetate can be synthesized through two different pathways. Firstly, acetyl-CoA can be produced by decarboxylation of pyruvate, then, acetyl-CoA is hydrolyzed to acetate by an acetyl-CoA hydrolase.80 Most of the acetate is produced by enteric bacteria, including Prevotella spp., Ruminococcus spp., Bifidobacterium spp., Bacteroides spp., Clostridium spp., Streptococcus spp., A. muciniphila, and B. hydrogenotrophica, using this pathway.81 Secondly, the Wood-Ljungdahl pathway can be also used by acetogenic bacteria to form acetate from acetyl-CoA. Here, the reduction of carbon dioxide generates carbon monoxide, which reacts with a coenzyme A molecule and a methyl group to produce acetyl-CoA. At the same time, acetyl-CoA is the substrate to obtain acetate.82
The mercapturic acid pathway
Published in Critical Reviews in Toxicology, 2019
Patrick E. Hanna, M. W. Anders
NAT8 was purified approximately three-fold from rat kidney microsomes, but the lability of the enzyme prevented further purification (Duffel and Jakoby 1982, 1985). An approximately 6-fold purification of the enzyme with a detergent-solubilization procedure has been reported, but again considerable activity was lost during purification (Aigner et al. 1996). Protein analysis indicated that NAT8 appeared to be a homodimer with a subunit molecular mass of 34 kDa, although the results of a later study indicated that NAT8 was likely a minor component of the enzyme preparation analyzed by Aigner et al. (Veiga-da-Cunha et al. 2010). An improved, detergent-based purification procedure that yielded an approximately 60-fold purification of pig kidney NAT8 has been reported, but the preparation contained considerable acetyl-CoA hydrolase activity (Kraus et al. 2000).
Molecular mechanisms of ethanol biotransformation: enzymes of oxidative and nonoxidative metabolic pathways in human
Published in Xenobiotica, 2020
Grażyna Kubiak-Tomaszewska, Piotr Tomaszewski, Jan Pachecka, Marta Struga, Wioletta Olejarz, Magdalena Mielczarek-Puta, Grażyna Nowicka
Acetic acid, which is a product of the reaction catalyzed by ALDH, is effectively released from liver cells to the peritoneal space, from where it enters the bloodstream. It is one of the factors determining the development of metabolic acidosis. This is despite the fact that in the cytosol of hepatocytes, acetyl-CoA synthetase (ACS, AceCS, AcCoAS, acetate:CoA ligase, EC 6.2.1.1) is present, which, interestingly, is one of the seven nickel metalloproteins identified in the body (Watt & Ludden, 1999). The cytoplasmic isoenzyme ACS1 (AceCS1) present in the liver is characterised by a high Km value in the reaction with acetate, which increases the importance of acetate activation to acetyl-CoA directly in the liver only at very high acetate concentrations (Fujino et al., 2001; Lumeng & Davis, 1973; Yamashita et al., 2001). At the same time, acetyl-CoA hydrolase (EC 3.1.2.1), present in cytosol, mitochondrial matrix and peroxisomes of hepatocytes, is activated by high concentrations of NADH + H+, which is a typical consequence of ethanol metabolism catalyzed by ADH and ALDH (ExPasy, 2020; Garras et al., 1995; Hovik et al., 1991; IUBMB, 2020; Yamashita et al., 2001). Thus, the likelihood of further use of metabolic acetate, formed as a result of ethanol biotransformation is close to zero in the liver itself. The situation is different in myocytes of the myocardium, where the mitochondrial isoenzyme of acetyl-CoA synthase (ACS2, AceCS2) shows a low Km value in comparison to the liver variant, with a low activity of acetyl-CoA hydrolase. Myocytes of skeletal muscles show a similar, but slightly less marked, enzymatic ability to use acetates. Thanks to the observed enzymatic differentiation, acetates released from the liver can become valuable energy and sometimes building substrates for heart muscle cells, skeletal muscle cells, and perhaps also for cells of other peripheral tissues. After activation to acetyl-CoA (Figure 10) they can be used as substrates in the Krebs cycle or, less commonly, in anabolic processes, e.g. synthesis of fatty acids (Fujino et al., 2001; Mittendorfer et al., 1998; Yamashita et al., 2001).