THE OXIDATION OF l-ARABINOSE BY PSEUDOMONAS SACCHAROPHILA

The importance of the pentoses in the physiology of plants and animals has been known since ribose and deoxyribose were identified as constituents of nucleic acids. Interest in pentose metabolism has been stimulated in the past few years by the discovery that ribose-5-phosphate and ribulosed-phosphate were integrant parts of the oxidative breakdown of glucose (1). The subject of pentose and pentose phosphate metabolism has been reviewed by Lampen (2) and Horecker (3). It has recently been found that the pentose, ribulose-1 ,Bdiphosphate, may play a fundamental role in the process of photosynthesis (4). A study of pentose metabolism in Pseudomonas saccharophila was undertaken as a result of the discovery that glucose is metabolized in this organism by a mechanism involving neither the Emden-Meyerhof scheme nor the pentose phosphates (5). Preliminary studies revealed that the oxidation of n-arabinose by this organism is strikingly different from that of glucose. In the experiments to be reported, it has been shown that this pentose can be converted to a-ketoglutarate by a series of reactions which appear to involve neither phosphorylated intermediates nor the tricarboxylic acid cycle. Methods1 Cells of P. saccharophila were grown on a liquid mineral medium described previously (6) with n-arabinose as the sole carbon source. Resting cell suspensions were prepared by centrifuging liquid cultures inoculated 18 to 24 hours previously, washing the cells twice, and resuspending them in 0.033