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Biological Process for Butanol Production
Published in Jay J. Cheng, Biomass to Renewable Energy Processes, 2017
Maurycy Daroch, Jian-Hang Zhu, Fangxiao Yang
Acidogenesis starts in two major branch points of the metabolism acetyl-CoA and butyryl-CoA. During the acid-producing phase, acetate and butyrate are produced from acetyl-CoA and butyryl-CoA with two analogous, yet distinct sets of enzymes. Formation of acetate from acetyl-CoA is a two-step reaction catalyzed by phosphate acetyltransferase (phosphotransacetylase) and acetate kinase. The first of the two reactions yields acetyl phosphate from acetyl-CoA; the second one dephosphorylates acetyl phosphate to acetate yielding ATP as the second product. Analogously, formation of butyrate from butyrate-CoA follows the same pattern catalyzed by phosphate butyryltransferase (phosphotransbutyrylase) and butyryl kinase. Reaction catalyzed by phosphate butyryltransferase yields butyryl phosphate, while subsequent dephosphorylation reaction yields butyrate and ATP. Although in principle C. acetobutylicum can also convert pyruvate to lactate under certain conditions, this reaction is not considered an acidogenic reaction as this pathway is not operational under normal conditions (Jones and Woods, 1986). The two main sets of reactions originating from acetyl- and butyryl-CoA are important sources of ATP for the metabolism, but yield in the formation of highly acidic byproducts (acetate, butyrate) that in high concentrations of fermentation become toxic to the cells and induce metabolic shift from acidogenesis to solvengenesis.
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Published in Girma Biresaw, K.L. Mittal, Surfactants in Tribology, 2017
Daniel K.Y. Solaiman, Richard D. Ashby, Girma Biresaw, K.L. Mittal
Once formed, the fatty acids are oxidized at the ω or ω-1 position by an reduced nicotinamide adenine dinucleotide phosphate (NADPH)-dependent cytochrome P450 monooxygenase enzyme, which results in a hydroxy fatty acid. This enzyme is one of a family of cytochrome P450 monooxygenases that have been found in different strains of Candida and have been classified into the CYP52 family of cytochrome P450 enzymes capable of hydroxylating alkanes and fatty acids [35]. Once the hydroxy fatty acids are created, the fatty acids are glycosidically attached to a glucose moiety at C-1′ through the action of glucosyltransferase I using uridine 5′-diphosphate (UDP)-glucose as the glucosyl donor [36]. Subsequently, a second glucose molecule is introduced into the molecule through another glycosidic linkage between C-2′ of the forming SL molecule and C-1′ of the newly attached glucose molecule. This second glucosyl-transfer may be catalyzed by a second glucosyltransferase enzyme (glucosyltransferase II), which has been purified but whose activities seem to be analogous [35,37]. This enzymatic action results in the non-acetylated free-acid form of the SL. At this stage, the free-acid form can be acetylated through the action of acetyltransferase enzymes utilizing acetyl-CoA as the acetyl donor or enzymatically converted to the 1′,4″ lactone through the action of a lactone esterase that can then be acetylated. Acetylation of the final SL products may involve acetyl-transfer to both, one, or neither of the 6′ and 6″ hydroxy groups resulting in di-, mono-, or non-acetylated structural variants.
Biotransformation of Xenobiotics in Living Systems—Metabolism of Drugs: Partnership of Liver and Gut Microflora
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2020
Acetylation is an important route of metabolism for certain drugs and a range of food-derived and environmental carcinogens with an aromatic amine (R-NH2) or a hydrazine structure (R-NH-NH2), which are converted to aromatic amides (R-NH-COCH3) and hydrazides (R-NH-NH-COCH3), respectively. Aryl N-acetyltransferases (NAT) are cytosolic conjugating enzymes which transfer an acetyl group from donor acetyl coenzyme A (AcCoA) to arylamine and arylhydrazines. These enzymes commonly catalyse drug deactivation. Similar to products of methylation, N-acetylated metabolites are less water-soluble compared to parent compounds. There are two known human isoenzymes known as NAT2, which is responsible for isoniazid (Fig. 6.17), hydralazine and procainamide metabolism and NAT1, which is more specific for p-aminosalicylate, p-aminobenzoic acid and the folate metabolite, p-aminobenzoylglutamate (Sim et al., 2014; Grant et al., 1997). Both NAT1 and NAT2 activities have been described also in the intestine (Hickman et al., 1998). In humans, NAT1 has a much wider tissue distribution than NAT2 (Sim et al., 2014). These enzymes were the first discovered drug metabolizing enzymes with genetic polymorphisms, thus establishing the basics of pharmacogenetics. Pharmacogenetic variations have important clinical implications related to therapeutic efficacy and occurrence of adverse drug reactions. Pharmacogenomics is known to play the key role in the metabolism of isoniazid, a first-line drug for the treatment of tuberculosis. There are great interindividual variations in the rate of acetylation due to differences in the concentrations of NAT2 enzyme in the liver and gut mucosa. Therefore, patients may be characterized phenotypically as being either rapid or slow acetylators. The slow acetylators more commonly experience toxicity from drugs due to higher blood levels of the drug, whilst fast acetylators may not respond adequately to isoniazid in the treatment of tuberculosis (Ramachandran and Swaminathan, 2012; Roy et al., 2008).
Epigenotoxicity: a danger to the future life
Published in Journal of Environmental Science and Health, Part A, 2023
Farzaneh Kefayati, Atoosa Karimi Babaahmadi, Taraneh Mousavi, Mahshid Hodjat, Mohammad Abdollahi
Histone acetylation mainly presents in promoters as well as at lower levels in the genome. This reaction has been widely studied as it is ubiquitous and occurs in the early stages of transcription and protein synthesis. Histone acetyltransferases (HATs) are a family of enzymes that facilitate these reactions.[19] Since only lysine residues can be acetylated, histone acetylation is found at the amino terminus of the four significant histones. It is commonly referred to as histone acetyltransferases, usually HAT or Kanamycin acetyltransferase (KAT).[11] HDAC is a factor that separates acetyl from histones, resulting in transcriptional suppression. Acetylation is a process that can increase gene expression in a short time. Mutation of lysine reduces HAT or histone acetylation transferase activity in gene transcription.[19] HDACs are classified into four groups: (1) class I HDACs (HDAC 1, 2, 3, and 8) are exclusively expressed in the nucleus; (2) class II HDACs (HDACs 4, 5, 6, 7, 9, and 10) are expressed in the nucleus and cytoplasm; (3) class III HDACs (sirtuins 1-7) are located in the nucleus (sirtuin 1-6-7); and (4) class IV (HDAC 11) is expressed both in the cytoplasm and nucleus.[11]