The number of proteins that have been shown to be S-nitrosated in vivo is increasing steadily, highlighting the importance of this redox based post translational modification. S-nitrosoglutathione reductase (GSNOR) reduces S-nitrosoglutathione (GSNO) to GSNHOH, removing GSNO from the cytosol. GSNOR has been linked to asthma in humans and plays a role in disease resistance in the model organism Arabidopsis thaliana. We became interested in Arabidopsis GSNOR after discovering an apparent genetic link between it and heat shock response. We expressed and purified recombinant Arabidopsis thaliana GSNOR from E. coli and determined its crystal structure to 1.5 Å resolution. While searching for an inhibitor of the enzyme as part of a drug discovery program, we discovered that it can be oxidized to an inactive state, through disulphide linkage of Cys369 and Cys372. Subsequent reduction of this disulphide bond with DTT restores the enzyme to an active state. Mutation of Cys369 and Cys372 to alanine leaves a functional enzyme that cannot be oxidized to an inactive form. The Km and Kcat for GSNO are 26 +/- 6 µM and 188 +/- 10 sec^-1 and 28 +/- 5 μM and 201 +/- 8 sec^-1 for the wild type and mutant respectively. We will present structures of this enzyme in both the oxidized (1.9 Å) and reduced (1.5 Å) forms.