Catalyzes the oxidation of (S)-lactate (L-lactate) to pyruvate with subsequent transfer of electrons to cytochrome c (PubMed:11914072). Is involved in the utilization of (S)-lactate as a sole source of carbon for growth (PubMed:3004948). Can also use ferricyanide as an electron acceptor in vitro (PubMed:4593578, PubMed:3004948). (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. kcat is 207 sec(-1) with cytochrome c as electron acceptor. kcat is 400 sec(-1) with ferricyanide as electron acceptor. Homotetramer. By L-lactate. Induced during respiratory adaptation. Consists of two discrete domains, an N-terminal cytochrome b domain from residues 81 to 179 and a C-terminal flavin-binding domain from residues 180 to 566. In addition there is an extended C-terminal tail (PubMed:2329585, PubMed:11914072). The cytochrome b domain is required for efficient cytochrome c reduction (PubMed:11914072). Inactivation of this gene leads to a deficiency in L-lactate dehydrogenase activity and consequently to the inability to use L-lactate as a sole source of carbon. Present with 4590 molecules/cell in log phase SD medium. 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.