The Entner-Doudoroff Pathway

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.

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. 

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. 

The PPP handles pentoses and is important for nucleotide (ribose-5-phosphate) and fatty acid biosynthesis (NADPH2). The Entner-Doudoroff pathway catabolizes glucose into pyruvate and glyceraldehyde-3-phosphate. It is important primarily in Gram negative prokaryotes. ... 

The enzymes placed in class IV are from bacteria mainly utilizing the Entner—Doudoroff pathway, and the ADP-Glc PPases are distinctively activated by Fru 6-P and pyruvate, with ADP, AMP, and P behaving as inhibitors. " Included in this group are Agrobacterium tumefaciens and Arthrobacter viscosus. Photosynthetic... 

The uptake of fructose occurs by active transport, while glucose, which can be utilized only by rare mutants, enters the cell by diffusion only. Fructose is degraded via the Entner-Doudoroff pathway and the products of this pathway are further oxidized via the usual routes of intermediary metabolism. The basic metabolism does not differ from that of other aerobic bacteria. The strains mentioned are even able to respire anaerobically with nitrate as a hydrogen acceptor they grow as denitrihers with fructose as the substrate. No anaerobic growth tms been observed under autotrophic conditions. 

---