In higher plant aldehyde oxidases (AO) appear to be homo- and heterodimeric assemblies of AO subunits with probably different physiological functions. In vitro, AO-gamma uses heptaldehyde, benzaldehyde, naphthaldehyde and cinnamaldehyde as substrates; AO-beta uses indole-3-acetaldehyde (IAAld), indole-3-aldehyde (IAld) and naphtaldehyde; the AAO2-AAO3 dimer uses abscisic aldehyde. H2O + indole-3-acetaldehyde + O2 = (indol-3-yl)acetate + H(+) + H2O2 Binds 2 [2Fe-2S] clusters. Binds 1 Mo-molybdopterin (Mo-MPT) cofactor per subunit. Strongly inhibited by iodoacetate, potassium cyanide (KCN), 2-mercaptoethanol, dithiothreitol (DTT), p-chloromercuribenzoate, menadione and estradiol. Weakly inhibited by 4'-(9-acridinylamino)methanesulfon-m-anisidine (mAMSA) and tritonX-100. Not affected by allopurinol. Kinetic values were obtained with the AO-gamma dimer. Optimum pH is 8. Optimum temperature is 50 degrees Celsius. Aldehyde oxidases (AO) are homodimers and heterodimers of AO subunits. AO-beta is a AAO1-AAO2 heterodimer; AO-gamma is a AAO2 homodimer. AAO2 also forms a dimer with AAO3. Weakly expressed in roots, leaves and seedlings. In seedlings, mostly expressed in lower part of hypocotyls. Detectable in seeds and mature siliques at low levels. Belongs to the xanthine dehydrogenase family.