Oxidase that catalyzes the oxidation of medium and long chain hydroxyacids such as 2-hydroxyhexadecanoate, 2-hydroxyoctanoate, 2-hydroxyhexanoate and 2-hydroxybutanoate, to the correspondong 2-oxoacids (PubMed:15683236, PubMed:3061453, PubMed:8508789). Its role in the oxidation of 2-hydroxy fatty acids may contribute to the general pathway of fatty acid alpha-oxidation (By similarity). Can also use mandelate as substrate (PubMed:3061453). 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 (PubMed:15683236, PubMed:3061453, PubMed:8508789). a (2S)-2-hydroxycarboxylate + O2 = a 2-oxocarboxylate + H2O2 2-hydroxyoctanoate + O2 = 2-oxooctanoate + H2O2 2-hydroxyhexadecanoate + O2 = 2-oxohexadecanoate + H2O2 2-hydroxyhexanoate + O2 = 2-oxohexanoate + H2O2 mandelate + O2 = H2O2 + phenylglyoxylate Binds 1 FMN per subunit. Is inhibited in vitro by CCPST (4-carboxy-5-(4-chlorophenyl)sulfanyl-1,2,3-thiadiazole). kcat is 0.99 sec(-1) for the oxidation of L-2-hydroxyoctanoate with DCIP instead of O2 as electron acceptor. kcat is 0.34 sec(-1) for the oxidation of L-2-hydroxyhexadecanoate with DCIP instead of O2 as electron acceptor (PubMed:15683236). kcat is 1.66 sec(-1) for the oxidation of DL-2-hydroxybutanoate with DCIP instead of O2 as electron acceptor (PubMed:8508789). Homotetramer (PubMed:8508789). Could also form homooctamer. Expressed in kidney. Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family.