Arabidopsis thaliana alcohol dehydrogenase is differently affected by several redox modifications

In plant cells, many stresses, including low oxygen availability or hypoxia, result in a higher production of reactive oxygen and nitrogen species. These molecules can lead to damages of cell macromolecules, including proteins via their cysteine thiol groups. In this study, researchers show the effect of different redox modifications on alcohol dehydrogenase from a model plant Arabidopsis thaliana. This enzyme catalyzes the last step of the ethanol fermentation pathway used by plants to cope with energy deficiency during hypoxic stress. The results showed that Arabidopsis suspension cell cultures had decreased enzyme activity upon exposure to hydrogen peroxide, but not to the thiol oxidizing agent diamide. The study also demonstrated a significant decrease in the activity of purified enzyme by treatments with hydrogen peroxide and nitric oxide donor. Treatments leading to the formation of a disulfide bond between alcohol dehydrogenase and glutathione had no negative effect on the enzyme activity. The study identified two cysteine sites that could make a stable disulfide bond with glutathione, suggesting redox sensitivity of these residues. Mutation of one cysteine residue to serine caused an almost complete loss of the enzyme activity while the other cysteine to serine mutant had increased specific activity. Incubation of alcohol dehydrogenase with enzyme cofactor or product prevented inhibition of the enzyme by hydrogen peroxide or nitric oxide donor. These results suggest that binding of ADH with its cofactors may limit availability of cysteine residues to redox modifications. The present study demonstrates that alcohol dehydrogenase from A. thaliana is subject to different redox modifications. These results indicate that, while the enzyme is sensitive to reactive oxygen and nitrogen species, the nature of the oxidizing compound ultimately determines the effect on the enzyme activity.