Substrate selectivity of human aldehyde oxidase 1 in reduction of nitroaromatic drugs

Evolution, expression, and substrate specificities of aldehyde oxidase enzymes in eukaryotes

“…The functional role of AOXs in the vertebrate organisms is still largely unknown, although the broad substrate specificity supports the idea that these enzymes are involved in numerous metabolic pathways. In addition to the substrates shown in Table 1, it has to be noted that under hypoxic conditions, AOXs can also catalyze the reduction of Noxides, sulfoxides, nitro-compounds and heterocycles (12,(70)(71)(72)(73). More recently, it was also demonstrated that AOXs hydrolyze amides (12,74,75).…”

“…Nitrocompounds are further prototypes of toxic agents with the potential to be metabolized by mammalian AOXs. Indeed, molecules containing a nitro functionality exemplify the ability of AOXs to act not only as oxidases, but also as reductases (13,73,(90)(91)(92). For instance, various AOX isoenzymes have the potential to reduce 2-nitrofluorene, 1-nitro-pyrene and 4nitrobiphenyl, three widespread pollutants, into the corresponding amines.…”

Site-Directed Mutagenesis at the Molybdenum Pterin Cofactor Site of the Human Aldehyde Oxidase: Interrogating the Kinetic Differences Between Human and Cynomolgus Monkey

“…Therefore, to remove any complexities raised by competition between the reductive substrates, we substituted oxygen with dantrolene as a reducing substrate of AO under anaerobic conditions to probe the reduction half-reaction in this enzyme (Amano et al, 2018) as described in the methods section. We chose dantrolene as the reducing substrate in this study based on the previous reports of this compound being metabolized by AO even under normal oxygen concentration as well as its lack of competition with oxidative substrates and having a high turn-over rate among other structurally similar reductive substrates of AO (Amano et al, 2018;Ogiso et al, 2018). Furthermore, dantrolene has a similar K m to oxygen with the K m of oxygen for hAO being estimated to be close to 2 M (Abbasi et al, 2019) and the Km of dantrolene being 5 M (data not shown).…”

“…Several other potentially important amino acid differences, especially the K661E at the gate 1 of the substrate access channel, as well as L812F which is another important amino acid difference pointing to the entrance of the active site pocket still remain to be considered at the MoCo site of AO (Coelho et al, 2015). However, recent publications regarding the AO nitro reduction, most notably the one by Paragas et al in which the FAD site has been suggested as the reductive site of this enzyme, has brought up the possibility of amino acids at this site also having an important role in causing this marked kinetic difference between the two species (Konishi et al, 2017;Paragas et al, 2017a;Amano et al, 2018;Ogiso et al, 2018). However, it is also important to note that there are two sites involved in playing this catalytic see-saw.…”

“…Until recently it was believed that reduction of other substrates, such as the ones containing nitro groups, by AO would only happen under anaerobic conditions (Li et al, 2009;Weidert et al, 2013;Maia et al, 2015). However, quite a few examples of aerobic nitro reduction have been presented in the literature in the past few years (Konishi et al, 2017;Amano et al, 2018;Ogiso et al, 2018). This has in turn brought up the possibility of a competition between the reductive substrates and the molecular oxygen at the FAD site (Paragas et al, 2017a).…”