The activity of the fermentative enzyme Alcohol Dehydrogenase 1 from Arabidopsis thaliana is differentially altered by several redox post-translational modifications.

Several environmental factors can lead to oxygen limitation in plants, causing hypoxia or anoxia. Paradoxically, hypoxia is also known to cause an increase in production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). An accumulation of these molecules can lead to oxidation of thiol groups on protein Cys residues. During hypoxia, plant cells rely on fermentative pathways to cope with the energy deficiency
caused by respiration failure. Here, we focus on the terminal enzyme of ethanol fermentation, Alcohol Dehydrogenase (ADH) from Arabidopsis thaliana. We have demonstrated that an oxidative treatment of A. thaliana suspension cell cultures with H2O2 leads to a significant decrease in ADH specific activity. We purified recombinant A. thaliana ADH1 and demonstrated that treatments with H2O2 and nitric oxide (NO)
led to significant decreases in catalytic activity. ADH1 inhibition by NO, but not H2O2, was reversed by DTT. We found that the binding of ADH1 to NAD+ or NADH prevents the enzyme from inhibition by ROS or RNS, suggesting that the coenzymes limit the availability of sensitive Cys residue(s). We have also shown that the treatment of recombinant ADH1 with oxidized or reduced glutathione in the presence of the glutathionylation promoting agent diamide led to protein S-glutathionylation without affecting the enzyme activity. Mass spectrometry analysis showed that two Cys residues in ADH sequence can be modified by glutathione, whereas six other Cys participate in intrachain disulfide bond formation. These results suggest that ADH is subject to several redox post-translational modifications that affect its enzymatic activity.