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Physiology of Ethanol Production by Zymomonas mobilis
Published in Ayerim Y. Hernández Almanza, Nagamani Balagurusamy, Héctor Ruiz Leza, Cristóbal N. Aguilar, Bioethanol, 2023
Laura Andrea Pérez-García, Cindy Nataly Del Rio-Arellano, David Francisco Lafuente Rincón, Norma M. De La Fuente-Salcido
Knowing the differences between the different metabolic routes that exist between the bacteria Z. mobilis and the yeast S. cerevisiae. Lack of different enzymes in the Zymomonas metabolic pathway is found as phosphofructokinase (Pfk) in the EMP pathway, phosphogluconate dehydrogenase (Pgd) and transaldolase (Tal) in the PPP pathway, as well as 2-oxoglutarate dehydrogenase complex (sucABCD) and malate dehydrogenase (Mdh) in the TCA cycle and this enzyme deficiency carry more carbon into the ethanol production pathway and highly efficient glycolysis resulting in the theoretical maximum ethanol production [34]. Zymomonas sp. strains have a temperature range of 25 to 31°C but there are strains reported that can grow at temperatures of 40°C. It has a wide range of pH 3.7–7.5 so it has a high tolerance to acidic pH´s. However, most strains of Zymomonas sp. grow up at an optimal pH of 5–7. Some strains of Zymomonas also can grow up at high concentration of glucose medium more than 200 gL–1 but there is other that can grow up in 400 gL–1 glucose medium [8]. Another important characteristic is that the ZM4 strain is facultative aerobic, so this bacterium can perform the metabolism for the production of bioethanol under aerobic conditions, however it is reported that the production is lower than in the anaerobic condition [35]. Also, Z. mobilis possess a high tolerance of ethanol like 11–16% v/v [29].
Asymmetric Reduction of C=N Bonds by Imine Reductases and Reductive Aminases
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Matthias Höhne, Philipp Matzel, Martin Gand
The first imine reductases employed for biocatalysis were found in organisms identified from a strain screening for bioreduction of (R)- or (S)-2-methyl-1-pyrroline 1 (Mitsukura et al., 2010). The (R)- and (S)-selective IREDs were then identified from two different Streptomyces sp. strains (Mitsukura et al., 2011; Mitsukura et al., 2013). Their amino acid sequences are similar to enzymes of the 6-phosphogluconate dehydrogenase/3-hydroxyisobutyrate dehydrogenase family of reductases. Most of the IREDs explored for biocatalytic applications belong to this family and were identified by sequence similarity in protein databases (Patil et al., 2018): >150 IREDs have been identified and some of them were studied extensively. Therefore, these enzymes have the widest proven synthetic potential today.
The Pentose Phosphates Pathway—Glucogenesis
Published in Jean-Louis Burgot, Thermodynamics in Bioenergetics, 2019
The enzyme catalyzing the reaction is the glucose-6-phosphate dehydrogenase. The lactone is hydrolyzed to the acid-6-phosphogluconate under the action of a specific lactonase (Figure 101): Structure of 6-phosphogluconate acid.Then, the 6-phosphogluconate acid undergoes oxidation and decarboxylation. The keto-pentose ribulose-5-phosphate is formed under the action of the enzyme 6-phosphogluconate dehydrogenase. It is interesting to notice that, then, there is formation of a second molecule of NADPH (Figure 102): 6-phosphogluconateacid→6-phosphogluconatedehydrogenaseD-ribulose-5-phosphateFormation of ribulose-5-phosphate.
The effect of NADPH oxidase inhibitor diphenyleneiodonium (DPI) and glutathione (GSH) on Isatis cappadocica, under Arsenic (As) toxicity
Published in International Journal of Phytoremediation, 2021
Zahra Souri, Naser Karimi, Parvaiz Ahmad
The activity of several NADP-dehydrogenases such as G6PDH and 6-phosphogluconate dehydrogenase (6PGDH), intricate in the pentose phosphate pathway (oxidative phase), as well as NADP-isocitrate dehydrogenase and the NADP-malic enzyme depend on NADP (Corpas and Barroso 2014; de Freitas-Silva et al.2017). Therefore, decline in NADP levels can disturb several metabolic pathways that regulate plants growth and development under stress condition (Corpas and Barroso 2014). Some types of NADP-dehydrogenases are regulated at different levels of activity and/or protein/gene expression (Liu et al.2007, 2013; Marino et al.2007; Corpas and Barroso 2014). In addition, the significance of some NADP-dehydrogenases has been established through reverse genetic studies in various plant species (Scharte et al.2009; Dal Santo et al.2012; Siddappaji et al.2013). Therefore, it seems that, the activity of NADP-dehydrogenases and appropriate presentation of the pentose phosphate pathway can play an important role on tolerance responses of Isatis plant grown under As stress. Moreover, hyperaccumulator plants can detoxify As through adopting the detoxification strategies like: (a) the reduction of As, synthesis of metal binding thiols such as PCs complexing with As and their compartmentalization/vacuolar sequestration to minimize the As levels (Karimi et al.2009; Zhao et al.2010; Tripathi et al.2012; Souri et al.2017), and (b) the triggering of antioxidative defense responses to counteract the As-induced oxidative damages (Zhao et al.2010; Souri et al.2018, 2020).
Progress in microbiology for fermentative hydrogen production from organic wastes
Published in Critical Reviews in Environmental Science and Technology, 2019
Khanna et al. (2011) studied the redirection of biochemical pathways for the enhancement of H2 production by Enterobacter cloacae. Since NADH is usually generated by catabolism of glucose to pyruvate through glycolysis, and then hydrogen is produced through the oxidation of NADH. However, the conversion of pyruvate to ethanol and acids like lactic acid and butyric acid consumes NADH. Thus, they attempted to redirect the biochemical pathways to block alcohol and some of the organic acids formation in E. cloacae IIT-BT 08, increase the concentration of available NADH for hydrogen production, hydrogen yield and hydrogen production rate obtained were 2.26 mol H2/mol hexose and 1.25 L H2/L/h, which were 1.2 and 1.6 times higher than the wild type strain. Xiong et al. (2018) introduced xylA (encoding for xylose isomerase) and xylB from Thermoanaerobacter ethanolicus to cellulolytic bacteria Clostridium thermocellum DSM 1313, achieved simultaneous fermentation of xylose, glucose, cellobiose and cellulose. The results showed that both hydrogen and ethanol production were enhanced by twice when xylose and cellulose was consumed simultaneously, and hydrogen yield of 1.2 mol/mol hexose was obtained. Sekar et al. (2017) enhanced the co-production of hydrogen and ethanol from glucose in Escherichia coli by activating pentose-phosphate pathway through deletion of phosphoglucose isomerase and overexpression of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, hydrogen and ethanol yield obtained by the mutant strain was enhanced by 1.2 and 2.05 times over the wild strain, which were 1.74 mol H2/mol hexose and 1.62 mol ethanol/mol hexose, respectively.