Subsystem: Entner-Doudoroff Pathway
This subsystem's description is:
The classical Entner-Douderoff (ED) pathway of bacteria (and a limited number of lower eukaryotes) starts with the phosphorylation of either glucose or its oxidized derivative gluconate. The generated 2-keto-3-deoxy-6-phosphogluconate (KDPG) is converted by an aldol cleavage, resulting in the formation of GAP and pyruvate. The triose phosphate is activated by Pi , and is further degraded to pyruvate by enzymes that are identical with those of the Embden-Meyerhof (EM) pathway. The main difference between the ED and EM pathways is that, in the former, both NADPH and NADH are formed (instead of 2 NADH in EM), and that substrate-level phosphorylation only yields a single ATP per glucose molecule (ref. 1,2).
ED-like pathways found in archaea are modified in two ways:
In semi-phosphorylative pathway (Variant code 2) 2-keto-3-deoxygluconate (KDG) is phosphorylated to KDPG by KDG kinase, instead of conversion of glucose to glucose 6-phosphate, common for eubacteria.
In non-phosphorylative pathway, none of hexose intermediates are phosphorylated, instead activation via phosphorylation occurs at the level of 2P-glycerate by D-glycerate 2-kinase (Variant code 3).
In several species both - semi-phosphorylative and non-phosphorylative ED pathways appear to be operational (Variant code 4) – like in Sulfolobus and Thermoproteus tenax
While semi-phosphorylative ED pathway (via KDPG) is expected to have a similar net result as the classic eubacterial route, there appears to be no net generation of ATP by the non-phosphorylative ED pathway (via KDG).
Note, that a gene encoding 6-phosphogluconolactonase (EC 220.127.116.11) is has not been experimentaly detected in several taxonomic groups, including Firmicutes. An interesting candidate (BC3368 in B. cereus) has been predicted for the genus Bacillus by Ivanova et al (2003). It’s widely spread homologs in other Gram(+)s species have been assigned with this function here as well.
Functional role "6-phosphogluconate dehydrogenase, decarboxylating (PglDH)" has been included in this SS merely as an indicator of the presence of functional Pentose Phosphate pathway in an organism.
For more information, please check out the description and the additional notes tabs, below
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