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The Chemical Work of Biosynthesis
Published in Jean-Louis Burgot, Thermodynamics in Bioenergetics, 2019
Living cells use the chemical energy of ATP to perform the chemical work of biosynthesizing cellular components from precursor molecules. They use the common intermediate principle. We have seen that this principle makes possible the conservation of oxidation-reduction energy as the phosphate bond energy of ATP. Recall, for example, the formation of sucrose from glucose and fructose (Chapter 33). Glucose-1-phosphate is formed by the enzymatic transfer of a phosphate group from ATP to glucose. The bond between glucose and phosphate has about the same Gibbs energy of hydrolysis as the glucosidic bond which links fructose and glucose in sucrose. Once formed, glucose-1-phosphate reacts enzymatically with fructose to produce sucrose. The latter is readily formed. The overall reaction is downhill. Its ∆G’ is frankly negative (∆G’ = −6270 J mol–1): ATP + glucose→ADP + glucose-1-phosphateglucose-1-phosphate + fructose→sucrose + phosphate
Comparative proteomic analysis revealed the metabolic mechanism of excessive exopolysaccharide synthesis by Bacillus mucilaginosus under CaCO3 addition
Published in Preparative Biochemistry & Biotechnology, 2019
Hongyu Xu, Zhiwen Zhang, Hui Li, Yujie Yan, Jinsong Shi, Zhenghong Xu
Exopolysaccharides are water-soluble polysaccharides that are secreted by special microorganisms outside the cell walls in the growth and metabolism and are easily separated from the cells and secreted into the environment.[1,2] The enzymes involved in the synthesis of extracellular polysaccharides are located at different sites of the microbial cells and can be divided into the following four different types. The first enzyme type is located intracellularly and composed primarily of kinases and mutases. The other typical enzymes are glucokinase, phosphoglucose mutase, and glucose, which produce glucose-6-phosphate under the action of glucokinase. Glucose-1-phosphate is formed by the action of phosphoglucose mutase. Most of the glyconucleotide precursors required for the synthesis of extracellular polysaccharides are derived from glucose-1-phosphate; thus, phosphorylation is important for the synthesis of extracellular polysaccharides.[3] Recent studies highlighted a signaling activity for the exopolysaccharides produced by the Bacillus subtilis eps operon. This polymer is recognized by the extracellular domain of a tyrosine kinase that activates its own synthetic pathway.[4] The second type of enzyme is located intracellularly and includes UDP–glucose pyrophosphorylase (UGP) and various epimerases. UGP catalyzes glucose-1-phosphate as an important precursor for the polysaccharide synthesis of UDP–glucose. Under the action of epimerase, UDP–glucose can produce other sugar nucleotide precursors.[5] The third type of enzyme is mostly located in cell membranes, such as glycosyltransferases. The sugar nucleotides are transported to a glycosyl lipid carrier and then assembled into oligosaccharide repeat units with the participation of a glycosyltransferase.[6] The fourth type of enzyme is located in the cell membrane or extracellularly and presumably associated with bacterial extracellular polysaccharide polymerization. After a macromolecular polysaccharide is produced, it is secreted extracellularly to form a mucin polysaccharide or attached to the surface of the cell to form a capsular polysaccharide.[7]