Positive transcriptional regulator that is absolutely required for the expression of lactate racemase (Lar) activity. Controls Lar expression by sensing the L-/D-lactate ration. Binds to a 16-bp palindromic sequence (Lar box motif) that is present in the larR-larA intergenic region, allowing transcription of the larABCDE operon. L-lactate acts as a positive effector on the binding and multimerization of LarR on DNA, while D-lactate antagonizes the positive effect of L-lactate. Multimerizes on DNA. Multimerization is required for transcription activation. Induced by L-lactate but not by a racemic mixture of DL-lactate. Makes part of the larR(MN)QO operon.