Catalyzes the oxidation of (S)-lactate (L-lactate) to pyruvate with subsequent transfer of electrons to cytochrome c. Also displays oxidase activity in vitro, catalyzing the oxidation of a broad range of 2-hydroxyacids, such as glycolate, (S)-lactate, 2-hydroxyoctanoate, (S)-2-hydroxyglutarate and to a lesser extent mandelate, to the corresponding 2-oxoacids, with a reduction of O2 to H2O2 (PubMed:34555022). However, the physiological activity of this enzyme is most likely to function as an L-lactate dehydrogenase. May be involved in the utilization of (S)-lactate as a sole source of carbon for growth (Probable). (S)-lactate + 2 Fe(III)-[cytochrome c] = 2 Fe(II)-[cytochrome c] + 2 H(+) + pyruvate a (2S)-2-hydroxycarboxylate + O2 = a 2-oxocarboxylate + H2O2 glycolate + O2 = glyoxylate + H2O2 (S)-lactate + O2 = H2O2 + pyruvate 2-hydroxyoctanoate + O2 = 2-oxooctanoate + H2O2 (S)-2-hydroxyglutarate + O2 = 2-oxoglutarate + H2O2 mandelate + O2 = H2O2 + phenylglyoxylate 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. 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.