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The pathways of glucose dissimilation in Pseudomonas aeruginosa Gronlund, Audrey Florence

Abstract

The non-phosphorylated oxidative pathway of glucose dissimilation has been established in Pseudomonas aeruginosa and evidence for phosphorylated pathways, other than the Embden-Meyerhof scheme, has been obtained. In the present study the non-phosphorylated and phosphorylated pathways of glucose degradation have been investigated with cell-free extracts of this organism. Gluconolactone was shown to be an intermediate in the oxidation of glucose to gluconic acid. The enzymatic hydrolysis of the lactone ring has an absolute magnesium ion, or divalent cation requirement. In the presence of phosphate buffer magnesium was chelated and effectively removed from participation in the enzymatic reaction. As has been reported in the literature, the product of glucose and gluconic acid oxidation was identified as 2-ketogluconate. In the presence of adenosine triphosphate (ATP), glucose and gluconate are phosphorylated and the kinases involved, therefore, link the non-phosphorylated with the phosphorylated pathways. The demonstration of triphosphopyridine nucleotide (TPN) linked dehydrogenases for glucose-6-phosphate and 6-phosphogluconate, as well as the production of glucose-6-phosphate and 3-phosphoglyceraldehyde from cell-free extracts with gluconate or ribose plus ATP, illustrated the presence of a functional pentose phosphate cycle in this organism. An active 6-phosphogluconate dehydrase and a 2-keto-3-deoxy-6-phosphogluconate aldolase were demonstrated by the production of pyruvic acid from 6-phosphogluconate and indicated the presence of the Entner-Doudoroff pathway. The oxidation of 3-phosphoglyceraldehyde to 3-phosphoglyceric acid initiated by a TPN specific 3-phosphoglyceraldehyde dehydrogenase, and the conversion of phospho-enol-pyruvate to pyruvic acid was shown. It is suggested that the trioses are immediately concerned in the observed CO₂ fixation by this organism. Fructose-1,6-diphosphate aldolase, fructose-1,6-diphosphate phosphatase and phosphohexoisomerase may be involved in the formation of glucose-6-phosphate from triose phosphates. A direct link between 2-ketogluconate and the phosphorylated pathways could not be shown but the reduction of the phosphate ester of the compound was demonstrated. The feasibility of 2-ketogluconate undergoing a 3:3 split is presented. No attempt has been made to estimate the relative importance of the various pathways of glucose dissimilation as it is felt that this is determined by the conditions and stages of growth of the organism.

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