THE OXIDATION OF l-ARABINOSE BY PSEUDOMONAS SACCHAROPHILA

R Weimberg,Michael Doudoroff

doi:10.1016/s0021-9258(18)65926-5

R Weimberg, Michael Doudoroff

Open Access

https://doi.org/10.1016/s0021-9258(18)65926-5

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Abstract

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

Highlights

Experiments with Resting Cell SuspensionsResting cell suspensions of P. saccharophila grown with L-arabinose as substrate oxidized L-arabinose, sodium pyruvatc, and sodium acetat.e rapidly
SaccharophiZu have demonstrated that the metabolism of n-arabinose in this organism proceeds by a mechanism entirely different from that described for the breakdown of glucose [5]
A delactonizing enzyme is present in crude preparations which hydrolyzes the y-lactone to n-arabonic acid

Summary

Experiments with Resting Cell Suspensions

Resting cell suspensions of P. saccharophila grown with L-arabinose as substrate oxidized L-arabinose, sodium pyruvatc, and sodium acetat.e rapidly. The melting point of the derivative prepared from t.he reaction mixture poisoned with iodoacetate was 221-223’. Calculations based on the CO2 production in the presence of iodoacetate showed that the carboxyl group of pyruvic acid was equilibrated to an extent of approximately 6.0 per cent with the labeled CO2 present at the end of the experiment. The carboxyl group of a-ketoglutarate formed in the presence of arsenite was equilibrated to an extent of about 1.2 per cent This suggests that CO2 is not an intermediate in the major pathway of synthesis of either pyruvate or a-ketoglutarate from arabinose, a conclusion which was supported by further experiments with cell-free preparations

Experiments with Enqme Preparations

Findings

DISCUSSION

SUMMARY