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Pseudomonas putida
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Maria Tsampika Manoli, Natalia Tarazona, Aranzazu Mato, Beatriz Maestro, Jesús M. Sanz, Juan Nogales, M. Auxiliadora Prieto
The de novo fatty acid intermediates are activated by the acyl carrier protein (ACP). The fatty acid synthesis starts with the acetyl-CoA carboxylation into malonyl-CoA by the acetyl-CoA carboxylase, the AccABCD complex [81]. Then, the malonyl-CoA is transesterified into malonyl-ACP by the malonyl-CoA: ACP transacylase, FabD [82]. The generated malonyl-ACP is further condensed into 3-ketoacyl-ACP by different 3-ketoacyl-ACP synthases. First, it is condensed by an acetyl-CoA molecule by FabH, then, in successive rounds of elongation, a new molecule of malonyl-ACP is condensed with the 3-acyl-ACP formed by FabB or FabF [83,84]. FabB has also been proposed to catalyze the decarboxylation of malonyl-ACP into acetyl-ACP [85]. The following step includes the reduction of 3-ketoacyl-ACP into (R)-3-hydroxyacyl-ACP by a 3-ketoacyl-ACP reductase, FabG [86], and the formation of a double bond into enoyl-ACP by 3-hydroxyacyl-ACP dehydratase, FabA, or FabZ [87]. Finally, one enoyl-ACP reductase, FabI, FabK, or FabL transforms the enoyl-ACP into 3-acyl-ACP [88]. The gene that codifies for enoyl-ACP reductase activity has not been identified in P. putida KT2440 [84].
Algal Biofuel: A Promising Alternative for Fossil Fuel
Published in Maniruzzaman A. Aziz, Khairul Anuar Kassim, Wan Azelee Wan Abu Bakar, Aminaton Marto, Syed Anuar Faua’ad Syed Muhammad, Fossil Free Fuels, 2019
Hoofar Shokravi, Zahra Shokravi, Maniruzzaman A. Aziz, Hooman Shokravi
Lipid biosynthesis in microalgae mainly takes place through both fatty acid synthesis and TAG synthesis, which occur in the chloroplast and the endoplasmic reticulum, respectively. The fatty acid and TAG biosynthetic pathways have been fully characterized in microalgae. Fatty acid synthesis is performed by two different enzymatic systems including acetyl-CoA carboxylase (ACCase) and fatty acid synthase (FAS). The first step for the biosynthesis of fatty acid is synthesized under the catalysis of ACCase, which transforms acetyl-CoA to malonyl-CoA. The second step is catalyzed by FAS complex. The malonyl moiety is transferred to acyl carrier protein (ACP) and makes malonyl-ACP, which is added to another acyl-ACP to form an acyl chain with two carbons longer. Further reactions lead to a saturated and unsaturated acyl chain with acyl carrier protein. When the chain reaches the appropriate length, acyl carrier protein is removed from fatty acid, yielding the complete fatty acid. Furthermore, the synthesis of TAG is performed by four enzymes, including glycerol-3- phosphate dehydrogenase (GPDH), lysophosphatidic acyltransferase (LPAAT), diacylglycerol acyltransferase (DGAT) and glycerol-3-phosphate acyltransferase (GPAT). Therefore, the overexpression of these genes has been used as a technique to promote lipid content [58–60].
Biochemical Pathways for the Biofuel Production
Published in Debabrata Das, Jhansi L. Varanasi, Fundamentals of Biofuel Production Processes, 2019
Debabrata Das, Jhansi L. Varanasi
TAGs are the predominant component of the oils extracted from the seeds or fruits of oleaginous plants like sunflower, oilseed rape, maize, and soybean. TAGs of higher plants contain acyl groups of palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linolenic acid (18:2), and α-linolenic acid (18:3). In these organisms, the fatty acid biosynthesis occurs in the stroma of plastids. The subsequent incorporation of fatty acids into the glycerol backbone leads to the biosynthesis of TAGs in the endoplasmic reticulum (ER) (Figure 4.1a). During fatty acid synthesis, the acetyl-CoA carboxylases (ACC) catalyze the irreversible carboxylation of acetyl-CoA to form malonyl-CoA. The malonyl group is then transferred to the acyl carrier protein (ACP), giving rise to malonyl-ACP, which is the primary substrate for fatty acid synthase complex. Repeated condensation of malonyl-ACP by the action of fatty acid synthase complex with the subsequent addition of two carbon units after each elongation leads to the formation of fatty acid-ACP complexes (like 16:0 ACP, 18:0 ACP, and 18:1 ACP). The type of acyl chain bound to ACP depends upon the type of enzyme present (mostly ketoacyl synthases I, II, and III) and varies in different plant species. The termination of fatty acid elongation is catalyzed by ACP thioesterases, which catalysis the hydrolysis of acyl-ACP to produce free fatty acids that are able to cross the plastidial envelope. These free fatty acids are then reactivated as acyl-CoAs in the cytosol and form the acyl-CoA pool, which provides the acyl donor for the acyl transferase reactions of the TAG assembly in the ER.
Effects of glycerol and glucose on docosahexaenoic acid synthesis in Aurantiochyrium limacinum SFD-1502 by transcriptome analysis
Published in Preparative Biochemistry & Biotechnology, 2023
Huaqiu Zhang, Xiangying Zhao, Chen Zhao, Jiaxiang Zhang, Yang Liu, Mingjing Yao, Jianjun Liu
In FAS pathway, the first step of fatty acid synthesis is the conversion of acetyl-CoA to malonyl-COA catalyzed by acetyl-CoA carboxylase (ACCase), which is the rate-limiting step of FAS pathway.[47] Transcriptome analysis (Figure 4) showed that the expression of ACCase in glucose was higher than that in glycerol (2.85 times, 1.29 times, 1.88 times) at three time points, indicating that FAS pathway metabolic flux using glucose as carbon source was higher than that in glycerol substrate. The FAS pathway was activated by glucose, and the expression of fatty acid synthase subunit alpha (FAS2) increased by 3.69, 1.35 and 1.50 times in 24 hr, 48 hr and 72 hr, which produce more saturated fatty acids. Besides, Glucose as the only carbon source also activated the elongation enzyme and △8-desaturase in the cell. When glycerol was used as carbon source to activate PKS pathway, PKS gene expression increased by 1.80 times, 2.00 times and 1.34 times at three time points compared with glucose, resulting in producing more long-chain polyunsaturated fatty acids. As shown in Figure 2, the proportion of saturated fatty acid C16 in glucose at 72 h was 46.19%, which was 1.53 times of that in glycerol (30.14%). The proportion of DHA in glycerol was 48.63%, which was 41.24% higher than that in glucose (34.43%).
Effects of mixotrophic cultivation on antioxidation and lipid accumulation of Chlorella vulgaris in wastewater treatment
Published in International Journal of Phytoremediation, 2020
Ran Li, Jie Pan, Minmin Yan, Jiang Yang, Wenlong Qin
The fatty acid synthesis pathway of mixotrophic C. vulgaris in wastewater is illustrated in Figure 5. Specifically, CO2 enters the chloroplast to produce glyceraldehyde triphosphate through the Calvin cycle. After that, the glycolytic pathway forms pyruvate, which releases a CO2 molecule and produces acetyl-CoA under the action of pyruvate dehydrogenase (PDH) (Avidan et al.2015). The first key reaction in fatty acid synthesis is the acetyl-CoA conversion to malonyl-CoA catalyzed by ACCase. Our results showed the ACCase activity was enhanced and contributed to the fatty acid accumulation of C. vulgaris cultured in wastewater. During heterotrophic metabolism, after a small molecule of organic matter (e.g., glucose) enters the cell, it is first converted to pyruvic acid by the glycolysis pathway and then by the fatty acid metabolism pathway (Gao et al.2014). Glucose can also be converted into ADPGlc and then into starch under the catalysis by AGPase. However, the activity of ACCase in mixotrophic C. vulgaris in wastewater was weakened, indicating more glucose molecules participate in fatty acid synthesis, causing lipid accumulation.
Mechanisms of beneficial effects of exercise training on non-alcoholic fatty liver disease (NAFLD): Roles of oxidative stress and inflammation
Published in European Journal of Sport Science, 2019
Parvin Farzanegi, Amir Dana, Zeynab Ebrahimpoor, Mahdieh Asadi, Mohammad Ali Azarbayjani
Numerous studies showed that exercise training significantly decreases intrahepatic fat contents. The underlying mechanism involves β-oxidation and lipogenesis (Figure 1). Recent investigations have indicated that exercise activity can regulate hepatic lipid metabolism by regulating hepatic β-oxidation and lipogenesis (Jeppesen & Kiens, 2012). Rector et al. (2008) indicated that exercise training increases hepatic fatty acid oxidation in NAFLD rats by increasing acetyl-coenzyme A carboxylase (ACC) phosphorylation and cytochrome c contents, indicating a possible enhancement of the final steps of oxidative phosphorylation. They also showed that exercise training decreases hepatic lipogenesis by reducing fatty acid synthase (FAS) and ACC contents (Rector et al., 2008). ACC is the committed step in fatty acid synthesis, catalysing the carboxylation of acetyl-CoA to form malonyl-CoA. ACC phosphorylation inhibits its activity and reduces formation of malonyl-CoA. Reduced content of malonyl-CoA is associated with increase in fatty acid oxidation and decrease in available substrate for FAS. Koves et al. (2005) found that exercise training increased the flux of both β-oxidation and tricarboxylic acid (TCA) cycle in the skeletal muscle. These data suggest that exercise training can enhance the complete oxidation of lipids in both the liver and the skeletal muscle.