1. The existence of two different ~-glucose-6-phosphate dehydrogenases in Pseudomonas Juorescens has been demonstrated. Based on their different specificity and their different metabolic regulation one enzyme is appointed to the Entner-Doudoroff pathway and the other to the hexose monophosphate pathway.2. A procedure is described for the isolation of that ~-glucose-6-phosphate dehydrogenase which forms part of the Entner-Doudoroff pathway (Entner-Doudoroff enzyme). A 950-fold purification was achieved with an overall yield of 44 %. The final preparation, having a specific activity of about 300 pmol NADH formed per min per mg protein, was shown to be homogeneous.3. The molecular weight of the Entner-Doudoroff enzyme has been determined to be 220000 by gel permeation chromatography, and that of the other enzyme (Zwischenferment) has been shown to be 265000.4. The p l of the Entner-Doudoroff enzyme has been shown to be 5.24 and that of the Zwischenferment 4.27. The Entner-Doudoroff enzyme is stable in the range of pH 6 to 10.5 and shows its maximal activity at pH 8.9.5. The Entner-Doudoroff enzyme showed specificity for NAD' as well as for NADP' and exhibited homotropic effects for D-glucose 6-phosphate. It is inhibited by ATP which acts as a negative allosteric effector. Other nucleoside triphosphates as well as ADP are also inhibitory.6. The enzyme catalyzes the transfer of the axial hydrogen at carbon-1 of P-D-glucopyranose 6-phosphate to the si face of carbon-4 of the nicotinamide ring and must be classified as B-side stereospecific dehydrogenase.In organisms of the genus Pseudomonas glucose 6-phosphate may be metabolized via the Entner-Doudoroff pathway, which is characterized by the dehydratation of 6-phospho-~-gluconate to 2-keto-3-deoxy-6- phospho-D-gluconate and its subsequent cleavage to pyruvate and ~-glyceraldehyde-3-phosphate [ 1,2]. Although it is the sole pathway of D-glucose 6-phosphate metabolism in Ps. saccharophila, the additional existence of the hexose monophosphate pathway has been demonstrated in other species of Pseudomonads [3 -51. Both these pathways have in common the initial dehydrogenation of D-glucose 6-phosphate at carbon-1 and the subsequent hydrolysis of 6-phospho-~-glucono-l,5-lactone. According to that, the overlapping catabolic Entner-Doudoroff and anabolic hexose monophosphate pathways must be susceptible to metabolic regulation. The activity of ~-glucose-6-phosphate dehydrogenase from a number of Pseudomonads has been demonstrated to be subject to metabolic control by ATP or related triphosphates [6-91. Furthermore in the case of Ps. multivorans two ~-glucose-6-phosphate dehydrogenases have been
