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MetNet - plant pathway - glycolysis I
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Pathway details: glycolysis I


General info Interaction details Linked pathways Protein-protein interactions
Notes
  Pathway was created on Mon Jul 29, 2013.
 Contributed by aracyc:
General Information: The glycolysis pathway represented here is also known as the 'Embden-Meyerhof-Parnas pathway'. First identified in yeast cells and mammalian tissue, it is now also seen as the 'central' metabolic pathway in plants, and can be found, if at least in part, in all organisms. Glycolysis has evolved as a catabolic anaerobic pathway that fulfills two essential functions: i) it oxidizes hexoses to generate ATP, reductants and pyruvate, and ii) it is an amphibolic pathway (pathway that involves both catabolism and anabolism) because it can reversibly produce hexoses from various low-molecular weight molecules. The ultimate purpose of the pathway is to convert carbon in its reduced form in storage carbohydrates (e.g. glycogen, and simpler carbohydrates such as sucrose, and ). In plants, glycolysis is the predominant pathway fueling respiration (see TCA cycle variation III (eukaryotic)) because, unlike animal mitochondria, plant mitochondria rarely respire fatty acids. In plants, this pathway occurs in two different subcellular locations: the cytosol and plastids, which are the sites of sucrose degradation III and starch degradation, respectively. Whereas the plastidic glycolysis pathway (this pathway) is identical to the conventional microbial glycolysis, the cytosolic pathway (see glycolysis IV (plant cytosol)) is slightly modified. These pathways can interact with one another though the action of highly selective transporters present in the inner plastid envelope |CITS:[Emes93]|. In chloroplasts in the dark, as well as in plastids of non-photosynthetic tissues, the primary function of glycolysis I (plastidic) is the degradation of to generate carbon skeletons, reductants and ATP for anabolic pathways such as that of fatty acid biosynthesis initiation I via acetyl-CoA biosynthesis (from pyruvate). In the cytosol, the same products are generated from the degradation of sucrose via glycolysis IV (plant cytosol). In developing oil seeds, phosphoenoylpyruvate derived from glycolysis IV (plant cytosol) is transported from the cytosol to plastids, where it is further converted to pyruvate then acetyl-CoA to fuel fatty acid and oil biosynthesis. The pathway starts with β-D-glucose-6-phosphate, which is made available from a variety of sources (in the plant plastids, it results from starch degradation). The first committed step of glycolysis is the reversible conversion of β-D-glucose-6-phosphate into D-fructose-6-phosphate by an hexose phosphate isomerase, which changes the pyranose configuration of glucose into the furanose configuration of fructose. The second step is catalyzed by a phosphofructokinase in the presence of ATP; this step is irreversible (in the cytosol of plants, see sucrose degradation III, an alternative enzyme uses diphosphate instead of ATP). The third step is catalyzed by an aldolase which cleaves fructose-1,6-bisphosphate into interconvertable (they are keto-enol tautomers) two three-carbon fragments: D-glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. The interconversion of these tautomers is facilitated by a triose phosphate isomerase. The following reaction, which adds one phosphate residue to D-glyceraldehyde-3-phosphate to form 1,3-diphosphateglycerate, is freely reversible and requires NAD+ and phosphate. The next step releases one molecule of ATP during the conversion of 1,3-diphosphateglycerate into 3-phosphoglycerate by a Mg2+-dependent glyceraldehyde-3-phosphate kinase. The next step requires little energy change and leads to the reversible transfer of a phosphate group from the 3- to the 2-hydroxyl group of glycerate, leading to the formation of 2-phosphoglycerate. The removal of a molecule of water by an enolase in the presence of Mg2+ converts 2-phosphoglycerate into phosphoenolpyruvate (PEP). The final step of glycolysis involves the ketolization of PEP to pyruvate by a pyruvate kinase, leading to the release of a molecule of ATP. Note on the sucrose-starch relationship: Sucrose and starch biosyntheses are compartmentalized. Sucrose is synthesized in the cytosol, whereas starch is produced in the plastids. The two metabolic route intersect however at the level of 3-phosphoglycerate, which can be translocated across the chloroplast membrane via a 3PGA/Pi translocator |CITS:[AVIGAD97]|.
  Parts of this pathway occur in:   cytosol     plastid stroma     plastid     nucleus     mitochondrion     apoplast   multiple locations  


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