Summary: The transport and catabolism of C-dicarboxylic acids have been further studied in MNF3841. Uptake of [C]succinate was induced in free-living cells of strain MNF3841 within 12 min of exposure to succinate and reached a maximum rate within 60 min. Free-living cells of strain MNF3841 oxidizing fumarate accumulated pyruvate when treated with arsenite, an inhibitor of pyruvate dehydrogenase. Generation of pyruvate from C-dicarboxylates was accomplished by malic enzyme. Although malic enzyme was present in free-living cells grown on sucrose, higher activities were observed when fumarate or -arabinose was the growth substrate. In crude extracts, malic enzyme activity required either NAD or NADP as cofactor, together with Mn, and was stimulated by K.

Bacteroids from pea nodules transported [C]succinate immediately after isolation, and contained twofold higher activities of both malic enzyme and pyruvate dehydrogenase than those found in fumarate-grown free-living cells. These data indicate that C-dicarboxylates are available to nodule bacteroids and that they are catabolized through the tricarboxylic acid cycle using malic enzyme and pyruvate dehydrogenase to generate acetyl-CoA.


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