Entner-Doudoroff pathway

Gluconolactonase [Lactonase] (3.1.1.17) is present. Phospogluconate dehydratase (4.2.1.12) is present. Phospho-2-keto-3-deoxy-gluconate aldolase (4.1.2.14) is present. 

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Phospho-2-keto-3-deoxygluconate aldolase, an enzyme in the Entner-Doudoroff pathway, that catalyzes the cleavage 6-phospho-2-keto-3-deoxy-D-gluconate to form pyruvate and D-glyceraldehyde 3-phosphate. 

The 2-keto-3-deoxy-6-phosphogluconate aldolase (KDPG aldolase EC 4.1.2.14) catalyzes the cleavage of the dehydration product of 6-phosphogluconate, (KDPG), into glyceraldehyde-3-phosphate and pyruvate in the Entner-Doudoroff pathway (Scheme 7, R = P03H2). This... 

An additional way of cleaving a six-carbon sugar chain provides the basis for the Entner-Doudoroff pathway which is used by Zymomonas lindneri and many other species of bacteria. Glucose 6-P is oxidized first to 6-phosphogluconate, which is converted by dehydration to a 2-oxo-3-deoxy derivative (Eq. 17-18,... 

The metabolism of free L-fucose (6-deoxy-L-galac-tose), which is present in the diet and is also generated by degradation of glycoproteins, resembles the Entner-Doudoroff pathway of glucose metabolism (Eq. 17-18). Similar degradative pathways act on D-arabinose and L-galactose.60... 

The 2-keto-3-deoxy-6-phospho-D-gluconate (11) aldolase (KDPGlc aldolase or KdgA EC 4.1.2.14) provides the basis of the Entner-Doudoroff pathway that is used by many species of bacteria for the degradation of 6-phosphogluconate... 

For organisms where the predominant pathway is the Entner-Doudoroff pathway, fructose-1,6-bis-P is not a major metabolite in glucose degradation (because glucose-6-P is converted first into 6-P-gluconate and then to 2-keto,3-deoxy,6-P-gluconate) the activators for their ADPGlc PPase are fructose-6-P and pyruvate (Preiss, 1969, 1984 Preiss and Romeo, 1989). 

Phosphogluconate dehydratase participates in the Entner-Doudoroff pathway, which plays a primary role in glucose metabolism in many microorganisms. The enzyme catalyzes the dehydration of 6-phosphogluconate to form 2-keto-3-deoxy-6-phosphpgluconate. 

Fig. 1. Pathways of glucose metabolism in eubacteria and eukaryotes. The three major catabolic pathways are the Embden-Meyerhof glycolytic sequence (solid lines), the Entner-Doudoroff pathway (heavy solid lines) and the pentose phosphate pathway (dashed lines). The sequence from glyceraldehyde 3-phosphate to pyruvate is common to all three pathways.

Fig. 3. Pathways of glucose catabolism in halophilic and thermophilic archaebacteria. The modified Entner-Doudoroff pathway of halophiles (solid lines) and the non-phosphorylated Entner-Doudoroff pathway of Sulfolobus sol/ataricus and Thermoplasma acidophilum (dashed lines) are shown in comparison with the classical Entner-Doudoroff pathway of eubacteria (heavy solid lines) from Fig. 1.

Hexose catabolism has been studied in detail in two thermophilic archaebacterial genera, Sulfolobus and Thermoplasma, organisms which are phenotypically close (they are both thermoacidophiles) but phylogenetically distinct. Interestingly, in both genera a further modification of the Entner-Doudoroff pathway has been found. 

De Rosa et al. [12] discovered that Sulfolobus solfataricus metabolises glucose via an Entner-Doudoroff pathway in which the 2-keto-3-deoxygluconate undergoes... 

In Tp. acidophilum we have also found the production of pyruvate and glyceraldehyde via a non-phosphorylated Entner-Doudoroff pathway [2,14]. Furthermore, we have demonstrated that the glyceraldehyde is oxidised to glycerate, which is then converted to 2-phosphoglycerate by glycerate kinase. Enolase and pyruvate kinase complete the production of a second molecule of pyruvate (Fig. 3). Again, we have characterised the pathway enzymically and by the identification of intermediates [14], and evidence for its in vivo operation has been gained from radiorespirometric studies [2]. 

As previously mentioned and in the earlier discussion of fermentation methanol, bacteria of the genus Zymomonas such as Z. mobilis are known to convert hexoses to ethanol at high yields and short residence times. These bacteria are facultative anaerobes that have fermentative capacity and convert only glucose, fructose, and sucrose to equimolar quantities of ethanol and CO2 the pentoses are not converted. The Entner-Doudoroff pathway is utilized instead of the Embden-Meyerhof pathway, and a net yield of 1 mol of ATP is generated, not 2 mol as in bakers yeast. But pyruvate is the same key intermediate. In Z. mobilis, it is decarboxylated by pyruvate decarboxylase to yield acetaldehyde which is then reduced to ethanol by alcohol dehydrogenase. 

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