Oxidase that catalyzes the oxidation of a broad range of 2-hydroxyacids to the corresponding 2-oxoacids, with a reduction of O2 to H2O2. Displays the highest activity with the long-chain fatty acid 2-hydroxydodecanoate and has intermediate activity with 2-hydroxyhexanoate, 2-hydroxyoctanote, and the short-chain hydroxyacid (S)-lactate (L-lactate). With much lower activity, it can also use glycolate, leucic acid, valic acid, and isoleucic acid as substrates in vitro. Cannot use 2-hydroxyhexadecanoate or D-lactate as substrates. May be involved in a general medium- and long-chain fatty acid catabolic pathway such as alpha-oxidation. a (2S)-2-hydroxycarboxylate + O2 = a 2-oxocarboxylate + H2O2 2-hydroxydodecanoate + O2 = 2-oxododecanoate + H2O2 2-hydroxyhexanoate + O2 = 2-oxohexanoate + H2O2 2-hydroxyoctanoate + O2 = 2-oxooctanoate + H2O2 (S)-lactate + O2 = H2O2 + pyruvate Lipid metabolism; fatty acid metabolism. Homotetramer. Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family.