Substrate specificity of guinea pig liver aldehyde oxidase and bovine milk xanthine oxidase for methyl- and nitrobenzaldehydes
Both aidehyde oxidase and xanthine oxidase catalyze the oxidation of a wide range of N-heterocycles and aldehydes. These enzymes are important in the oxidation of N-heterocyclic xenobiotics, whereas their role in the oxidation of xenobiotic aldehydes is usually ignored. The present investigation describes the interaction of methyl- and nitrosubstituted benzaldehydes, in the ortho-, meta- and parapositions, with guinea pig liver aldehyde oxidase and bovine milk xanthine oxidase. The kinetic constants showed that most substituted benzaldehydes are excellent substrates of aldehyde oxidase with lower affinities for xanthine oxidase. Low K-m values for aldehyde oxidase were observed with most benzaldehydes tested, with 3-nitrobenzaldehyde having the lowest K-m value and 3-methylbenzaldehyde being the best substrate in terms of substrate efficiency (K-s). Additionally, low K-m values for xanthine oxidase were found with most benzaldehydes tested. However, all benzaldehydes also had low V-max values, which made them poor substrates of xanthine oxidase. It is therefore possible that aldehyde oxidase may be critical in the oxidation of xenobiotic and endobiotic derived aldehydes and its role in such reactions should not be ignored.