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. Author manuscript; available in PMC: 2016 Oct 11.
Published in final edited form as: Nat Genet. 2016 Apr 11;48(5):544–551. doi: 10.1038/ng.3548

Figure 3.

Figure 3

Alanine metabolism pathway in M. tuberculosis. L-alanine-dehydrogenase catalyzes the NAD-dependent interconversion between L-alanine and pyruvate. Under aerobic conditions this reaction allows for the utilization of L-alanine as a nitrogen source, whereas under hypoxic conditions this reaction allows for NADH recycling to NAD+. Separately, the initial step of peptidoglycan synthesis involves conversion of L-alanine to D-alanine by alanine racemase. Two D-alanine molecules are joined by D-ala-D-ala ligase to produce the dipeptide D-alanine-D-alanine, which is subsequently incorporated into the pentapeptide chain of the peptidoglycan cell wall. Both alanine racemase and D-ala-D-ala ligase are competitively inhibited by D-cycloserine, an analog of D-alanine.