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 leucic acid (2-hydroxy-4-methylpentanoate) and has intermediate activity with 2-hydroxyhexanoate and 2-hydroxyoctanote. Shows lower activity with 2-hydroxydodecanoate, valic acid, and isoleucic acid and extremely low activity with glycolate and L-lactate. Cannot use 2-hydroxyhexadecanoate or D-lactate as substrates. May be involved in the conversion or degradation of 2-hydroxyacids produced during the metabolism of fatty acids or amino acids. a (2S)-2-hydroxycarboxylate + O2 = a 2-oxocarboxylate + H2O2 2-hydroxy-4-methylpentanoate + O2 = 4-methyl-2-oxopentanoate + H2O2 2-hydroxyhexanoate + O2 = 2-oxohexanoate + H2O2 2-hydroxyoctanoate + O2 = 2-oxooctanoate + H2O2 Homotetramer. Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family.