Oxidase that catalyzes the oxidation of a broad range of 2-hydroxyacids to the corresponding 2-oxoacids, with a reduction of O2 to H2O2. 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 Lipid metabolism; fatty acid metabolism. Homotetramer (By similarity). Binds to CATB and CATC; these interactions are disturbed by alpha-hydroxy-2-pyridinemethanesulfonic acid (HPMS) and salicylic acid (SA) (PubMed:26900141). Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family.