The wild-type NAD-dependent malic enzyme () gene of (now ) was cloned and localized to a 3.1 kb region isolated on the cosmid pTH69. This cosmid complemented the symbiotic nitrogen fixation (Fix) phenotype of mutants. The gene was mapped by conjugation to between the and markers on the chromosome. β-Galactosidase activities measured in bacterial strains carrying either or gene fusions (the gene encodes NADP-dependent malic enzyme) indicated that the gene was expressed constitutively in free-living cells and in N-fixing bacteroids whereas expression of the gene was repressed in bacteroids. The gene product (DME) was overexpressed in and partially purified from The properties of this enzyme, together with those of the NADP-dependent malic enzyme (TME) partially purified from mutants, were determined. Acetyl-CoA inhibited DME but not TME activity. This result supports the hypothesis that DME, together with pyruvate dehydrogenase, forms a pathway in which malate is converted to acetyl-CoA.


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