Oxidase that catalyzes the oxidation of medium and long chain hydroxyacids such as 2-hydroxyhexadecanoate and 2-hydroxyoctanoate, to the correspondong 2-oxoacids (PubMed:10777549). Its role in the oxidation of 2-hydroxy fatty acids may contribute to the general pathway of fatty acid alpha-oxidation (Probable). Active in vitro with the artificial electron acceptor 2,6-dichlorophenolindophenol (DCIP), but O2 is believed to be the physiological electron acceptor, leading to the production of H2O2. Is not active on glycolate, glyoxylate, L-lactate and 2-hydroxybutanoate (PubMed:10777549). a (2S)-2-hydroxycarboxylate + O2 = a 2-oxocarboxylate + H2O2 2-hydroxyhexadecanoate + O2 = 2-oxohexadecanoate + H2O2 2-hydroxyoctanoate + O2 = 2-oxooctanoate + H2O2 Lipid metabolism; fatty acid metabolism. Homotetramer. Expressed in the liver and kidney. Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family.