Catalyzes the oxidation of (S)-lactate (L-lactate) to pyruvate with subsequent transfer of electrons to cytochrome c. Is involved in the utilization of (S)-lactate as a sole source of carbon for growth. (S)-lactate + 2 Fe(III)-[cytochrome c] = 2 Fe(II)-[cytochrome c] + 2 H(+) + pyruvate Binds 1 heme b (iron(II)-protoporphyrin IX) group non-covalently per subunit. Homotetramer. Consists of two discrete domains, an N-terminal cytochrome b domain and a C-terminal flavin-binding domain. In addition there is an extended C-terminal tail. The cytochrome b domain is required for efficient cytochrome c reduction. In the N-terminal section; belongs to the cytochrome b5 family. In the C-terminal section; belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family.