METABOLISM OF DICARBOXYLIC ACIDS IN ACETOBACTER XYLINUM

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Abstract
During the oxidation of fumarate or L-malate by whole cells or extracts of Acetobacter xylinum grown on succinate, a keto-acid accumulated in the medium in considerable amounts. This acid was identified as oxaloacetic-acid (OAA). No accumulation of OAA was observed when succinate served as substrate. These phenomena could be explained by the kinetics of malate, succinate and OAA oxidation. OAA did not inhibit malate oxidation, even when present at high concentrations. When cells were incubated with OAA or fumarate in the presence of C14O2, only the beta-carboxyl of residual OAA was found to be labeled. Evidence was obtained indicating that nicotinamide-adenine-dinucleotide (NAD) or nicotinamide-adenine-dinucleotide -phosphate (NADP) are not directly involved in malate oxidation by cell-free extracts. The results suggest that malate oxidation in A. xylinum is irreversible, and is catalyzed by an enzyme which is not NAD- or NADP-linked.