Carbohydrate Oxidation by Pseudomonas Fluorescens Ii. Mechanism of Hexose Phosphate Oxidation* by W. A. Wood

Glucose oxidation by Pseudomonas Jluorescens (1) and Pseudomonas aeruginosa (2) has been shown to proceed via gluconate to 2-ketogluconate without the involvement of phosphorylated intermediates. 2-Ketogluconate is oxidized further in growing cultures (3) and resting cell suspensions (4), but attempts to obtain dried cell preparations or cell-free extracts which oxidize 2-ketogluconate have been successful only with Acetobacter melanogenum, in which case 2,5-diketogluconate was formed (5). The rapid oxidation of glucose-l-phosphate (G-l-P), glucose-6-phosphate (G-6-P), and fructose-6-phosphate (F-6-P) by extracts of P. Jluorestens, observed by Wood and Schwerdt (I), has suggested the existence of other pathways of carbohydrate oxidation in addition to direct oxidation via gluconate and 2-ketogluconate. In addition, the presence of phosphoglucomutase, phosphohexose isomerase, and hexokinase in Pseudomonas putrefaciens and enzymes converting 6-phosphogluconate to pyruvate and triose phosphate in Pseudomonas saccharophila have been demonstrated by Klein and Doudoroff (6) and Entner and Doudoroff (7). These findings further indicate the presence of oxidative pathways involving phosphorylated intermediates in the pseudomonads. In the latter two organisms, however, the oxidation of glucose to gluconate and 2-ketogluconate apparently does not occur. In view of the apparent multiplicity of oxidative pathways in these organisms, further experiments have been undertaken to elucidate the mechanism of hexose phosphate oxidation. The data to be presented indicate the existence of alternative routes of phosphate ester metabolism in P. Jluorescens. In the oxidative (hexose monophosphate) pathway, 6-phosphogluconate undergoes both an oxidation and a non-oxidative split to pyruvate and triose phosphate. The presence of several glycolytic en-