Formation of Pentose Phosphate from 6-Phosphogluconate

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Abstract
The action of yeast enzymes on 6-phosphogluconate was studied in the presence of triphosphopyridine nucleotide, phenazine as hydrogen carrier, 0.01 [image] pH 7 phosphate buffer, and 0.0067 [image] NaCN which promoted the oxidation. The end products and intermediates in the resulting reactions were fractionated following precipitation of the proteins by 5% trichloracetic acid; phosphate esters were isolated as Ba salts by precipitation in 80% ethanol, and analyzed by paper chromatography in 80% ethanol containing 0.8% acetic acid (pH 3.5) or 0.64% boric acid. At the end of the reaction slightly over 0.5 mole of O2 had been consumed, 0.5 mole of CO2 produced, and 0.25-0.40 mole of new pentose had appeared for each mole of 6-phosphogluconate present. The formation of glyceraldehyde-3-phosphate and disappearance of 6-phosphogluconate were also demonstrated. Direct fermentation analysis in Warburg apparatus using Escherichia coli strains specifically adapted to ribose or D-arabinose revealed ribose amounting to 25% of the pentose produced. However, 50% of the Bial-reactive phosphate formed did not have the chromatographic properties of either ribose- or arabinose-5-phosphate. Evidently this system contains enzymes for at least 2 reaction steps: one oxidation involving the disappearance of 0.5 mole of 6-phosphogluconate did not result in pentose formation; the oxidation of the remaining 0.5 mole of substrate resulted in decarboxylation and pentose phosphate formation.