Succinate Metabolism of Isolated Soybean Nodule Bacteroids at Low Oxygen Concentration

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The effects of various concentrations of succinate in the incubation system on ARA and oxidative succinate degradation by nodule bacteroids were analyzed. When the bacteroids' ARA was measured in various concentrations of succinate the highest ARA was observed at 2mM succinate, and the activity was lower at higher succinate concentrations.
To monitor the oxidative degradation of exogenous 2, 3-¹⁴C-succinate by nodule bacteroids the formation of ¹⁴CO₂ was measured continuously with or without Lb.
In 1% oxygen ¹⁴CO₂ was formed actively by bacteroids at 0.5 to 3mM succinate, but at 4 or 8 HIM succinate the bacteroid's ¹⁴CO₂ formation was almost negligible. The bacteroids did not release ¹⁴CO₂ with no oxygen in the incubation system.
Addition of Lb (100mM) to the incubation system stimulated the ¹⁴CO₂ formation at all concentrations of succinate in 1% O₂, especially at 4 or 8 mM succinate the succinate oxidation was greatly improved.
The pathway of succinate degradation in the bacteroids was analyzed when the incubation system contained 2, 3-¹⁴C-succinate and 100μ Lb in 1% O₂. The succinate fed was metabolized actively, and the labelling was incorporated mainly into TCA cycle member organic acids, though one major peak was not identified.
The data suggest that the exogenous 2, 3-¹⁴C-succinate was mainly oxidized through the TCA cycle in bacteroids, and Lb is important in stimulating succinate oxidation and ARA when the succinate concentration is higher than 3 mM.