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Biosynthesis of Starch
Published in Jean-Luc Wertz, Bénédicte Goffin, Starch in the Bioeconomy, 2020
Jean-Luc Wertz, Bénédicte Goffin
In photosynthetically active chloroplasts of leaves (Figure 3.5a), the generation of ADPglucose is directly linked to the Calvin–Benson Cycle through the conversion of fructose-6-phosphate to glucose-6-phosphate (G6P) (catalyzed by phosphoglucose isomerase) through to G1P (catalyzed by phosphoglucomutase).14, 17 AGPase (EC 2.7.7.27) then catalyzes the conversion of G1P and ATP to ADPglucose and pyrophosphate (PPi). Through this pathway, approximately 30%–50 % of photoassimilates of Arabidopsis leaves are partitioned into starch. Each of the aforementioned reactions is thermodynamically reversible. However, in vivo, the PPi product of the last reaction is further metabolized; it is hydrolyzed to yield two molecules of orthophosphate (Pi). This renders the synthesis of ADPglucose in the chloroplast essentially irreversible.
Biological Process for Ethanol Production
Published in Jay J. Cheng, Biomass to Renewable Energy Processes, 2017
Under the catalysis of phosphoglucose isomerase, glucose-6-phosphate is isomerized to fructose-6-phosphate. This is a reversible reaction and the ratio of glucose-6-phosphate to fructose-6-phosphate is normally 7:3 at equilibrium. However, the reaction rate is very high.
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.