6- P gluconate

Glucose 6-phosphate Gluconolactone 6-(p) Gluconate 6-phosphate Ribulose 5-phosphate... 

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). 

Next Gluconolactonase opens the ring with the addition of a molecule of water. Then 6-P-gluconate DH oxidizes the 3 carbon to a ketone. This results in the 2 carbon becoming somewhat acidic, thus destabilizing the carboxyl group, which is then lost to give the five carbon ribulose-5-P. 

Fig, 17.6 Hexose monophosphate pathway. 1, glucose-6-P-dehydrogenase 2, 6-P-gluconolactonase 3,6-P-gluconate dehydrogenase 4, phosphoribose isomerase 5, phosphoketopentose epimerase 6, transketolase 7, transaldolase TPP, thiamine pyrophosphate. 

The oxidation of glucose to 5-p-ribulose involves in order phosphorylation by ATP oxidation of the sugar aldehyde to the lactone by TPN and finally oxidative decarboxylation of 6-p-gluconate to 5-p-ribulose again with TPN as specific electron acceptor. Phosphogluconate can be conceived of as a /3-hydroxy acid which serially is oxidized to the corresponding /3-keto acid and then decarboxylated to 5-p-ribulose. Both the oxidation and the corresponding decarboxylation appear to be catalyzed by the same enzyme. 

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