Xanthine dehydrogenase AtXDH1 from Arabidopsis thaliana is a potent producer of superoxide anions via its NADH oxidase activity

Abstract

Xanthine dehydrogenase AtXDH1 from Arabidopsis thaliana is a key enzyme in purine degradation where it oxidizes hypoxanthine to xanthine and xanthine to uric acid. Electrons released from these substrates are either transferred to NAD(+) or to molecular oxygen, thereby yielding NADH or superoxide, respectively. By an alternative activity, AtXDH1 is capable of oxidizing NADH with concomitant formation of NAD(+) and superoxide. Here we demonstrate that in comparison to the specific activity with xanthine as substrate, the specific activity of recombinant AtXDH1 with NADH as substrate is about 15-times higher accompanied by a doubling in superoxide production. The observation that NAD(+) inhibits NADH oxidase activity of AtXDH1 while NADH suppresses NAD(+)-dependent xanthine oxidation indicates that both NAD(+) and NADH compete for the same binding-site and that both sub-activities are not expressed at the same time. Rather, each sub-activity is determined by specific conditions such as the availability of substrates and co-substrates, which allows regulation of superoxide production by AtXDH1. Since AtXDH1 exhibits the most pronounced NADH oxidase activity among all xanthine dehydrogenase proteins studied thus far, our results imply that in particular by its NADH oxidase activity AtXDH1 is an efficient producer of superoxide also in vivo.

Antioxidant activity of methanol extracts of different parts of Lantana camara

“…Xanthine oxidase is a flavoprotein, which catalyses the oxidation of hypoxanthine to xanthine and generated superoxide and uric acid [16] . It has exhibited that xanthine oxidase inhibitors may be useful for the treatment of hepatic disease and gout, which is caused by the generation of uric acid and superoxide anion radical [17] .…”

Glutaredoxin GRXS17 Associates with the Cytosolic Iron-Sulfur Cluster Assembly Pathway

“…XDH1 belongs to the family of xanthine oxidoreductases (XORs) that catalyze the oxidation of hypoxanthine and xanthine to uric acid during purine degradation. XDH1 is active as a homodimer in which each monomer has four cofactors: two [2Fe-2S] prosthetic groups, one FAD molecule, and one molybdenum cofactor (Moco), bound to the N-terminal, central, and C-terminal part of the protein, respectively (Zarepour et al, 2010).…”

“…Because XDH1 contains two [2Fe-2S] cofactors that are required for electron transfer to reduce the substrates xanthine and hypoxanthine (Zarepour et al, 2010), we investigated the GRXS17-XDH1 interaction in more detail. Interaction between XDH1 and GRXS17 was confirmed in a Y2H assay ( Fig.…”

Xanthine dehydrogenase: An old enzyme with new knowledge and prospects

“…Several XDH genes have been cloned and expressed in exogenous hosts, which includes the rat liver XDH expression in insect cell system, A. thalianas XDH in Pichia pastoris, and R. capsulates and A. baumannii XDHs in E. coli. 6,17,18 A recombinant E. coli XDH can even be obtained from Sigma Company in the market. However, all the commercial XDHs are suffered in low catalytic activity and efficiency, in comparison to other industrial enzymes with hundreds of thousands of turnover numbers.…”

“…15,16 A few XDH genes have also been cloned and expressed in different hosts. 6,17,18 The bacterial XDHs usually show better catalytic activity and thermal stability than that of eukaryotic XDHs, however, both of them display optimum catalytic activity at nearly neutral pH and relatively low temperatures, and very limit pH-activity range, which limit their biotechnological applications (see the review 19 ). In this addendum, we would describe the latest developments of occurrence, biosynthesis, structure, production, and the potential applications of the XDHs.…”