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Tailoring Triacylglycerol Biosynthetic Pathway in Plants for Biofuel Production
Published in Arindam Kuila, Sustainable Biofuel and Biomass, 2019
Kshitija Sinha, Ranjeet Kaur, Rupam Kumar Bhunia
β-oxidation of fatty acid is the process of cleavage of fatty acid carbon units into acetyl-CoA moieties, and it occurs in glyoxysome (Bewley, 2001). The glyoxysome contains the enzymes involved in this β-oxidation pathway, that is, acyl-CoA oxidase (ACX), multifunctional protein (MFP), and 3-ketoacyl-CoA thiolase (KAT). These enzymes catalyze oxidation, hydration and dehydrogenation, and thiolytic cleavage reactions, respectively (Graham, 2008). Other reactions are also involved which are required for the breakdown of unsaturated fatty acids with double or triple bonds in the cis configuration at even- and odd-numbered carbons in the chain. The enzymatic activity of ACX leads to the production of hydrogen peroxide which is a kind of reactive oxygen species and is necessary to be detoxified. This detoxification happens with the help of a catalase enzyme located inside the peroxisome or by ascorbate peroxidase (APX) present on the membrane of peroxisomes (Pracharoenwattana, 2010). After the breakdown of the fatty acids via β-oxidation, the acetyl-coA undergoes a sequence of reactions, altogether called the glyoxylate cycle, in which succinate and oxaloacetate are formed. The enzymes involved in this cycle such as citrate synthase, aconitase, and malate dehydrogenase also participate in the citric acid cycle. However, two enzymes known as isocitrate lyase and malate synthase work only for the glyoxylate cycle in bypassing the steps of decarboxylation in the citric acid cycle (Beevers, 1980). These two enzymes generate malate and succinate, both of which are the citric acid cycle intermediates which can be converted to oxaloacetate. Out of the two molecules of oxaloacetate formed here, one can rejoin the glyoxylate cycle while the other participates in gluconeogenesis (Beevers, 1980).
Integrated Models
Published in Markus W. Covert, Fundamentals of Systems Biology, 2017
Let’s turn to our glucose uptake/acetate reutilization example for an example. One of the genes required for acetate reutilization that is down-regulated when glucose is present is aceA, which encodes the isocitrate lyase enzyme AceA. CRP is the transcription factor that induces aceA expression. As you know, CRP-based regulation is complicated (Figures 1.1 and 7.1), but for now we’ll just say that CRP is inactive when glucose is present.
Proteomics investigation of molecular mechanisms affected by EnBase culture system in anti-VEGF fab fragment producing E. coli BL21 (DE3)
Published in Preparative Biochemistry and Biotechnology, 2019
Bahareh Azarian, Amin Azimi, Mahboubeh Sepehri, Vahideh Samimi Fam, Faegheh Rezaie, Yeganeh Talebkhan, Vahid Khalaj, Fatemeh Davami
Metabolism of isocitrate for continuing the TCA cycle or entering glyoxylate cycle is determined by regulation of two enzymes: isocitrate lyase and isocitrate dehydrogenase. Isocitrate lyase leads isocitrate to glyoxylate cycle and cleaves it to glyoxylate and succinate. Glyoxylate is finally converted to oxaloacetate to start a new glyoxylate cycle. The succinate may be converted into oxaloacetate through malate and be used for biosynthetic purposes. Several studies have reported up-regulation of isocitrate lyase and other glyoxylate cycle enzymes in cells cultivated in glucose-limited condition.[29–31] Fischer reports the PEP-glyoxylate cycle in E. coli and its higher rate of activity in glucose-limited cells.[29] The three enzymes of this cycle are isocitrate lyase and malate synthase from glyoxylate cycle and phosphoenolpyruvate carboxykinase (Pck). This cycle results in higher production of oxaloacetate, and the activity of Pck converts oxaloacetate to PEP which can be further metabolized for gluconeogenesis or as a precursor of amino acid biosynthesis. Isocitrate lyase and Pck, two enzymes of PEP-glyoxylate cycle, are up-regulated in EnBase-mode-cultured cells in the 6 hr phase, which is consistent with their higher biosynthetic activity and protein expression of cells in this phase. By continuing the culture for 24 hr, only the Pck was found to be up-regulated. EnBase-mode-cultured cells have elevated catabolic activity for degradation of aggregated plasmid-encoded protein in low growth-rate phase.[9] This catabolic activity leads to elevated gluconeogenesis of PEP as a product of the Pck.