Catalyzes the oxidative decarboxylation of (S)-lactate (L-lactate) to acetate and carbon dioxide. Its physiological role remains unknown. (S)-lactate + O2 = acetate + CO2 + H2O Binds 1 FMN per subunit. kcat is 6250 min(-1). Homotetramer. This enzyme proceeds along a 'coupled pathway', wherein rather than releasing the alpha-keto-acid as a product (in this case pyruvate), it remains in the active site, and after reaction with hydrogen peroxide undergoes an oxidative decarboxylation to produce acetate, carbon dioxide, and water. Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family. This enzyme was originally referred to as 'lactate oxidase' but this acetate producing enzyme is now referred to as 'lactate monooxygenase' (LMO), and 'lactate oxidase' (LOX) refers to a related flavoenzyme that converts lactate and molecular oxygen to pyruvate and hydrogen peroxide.