Effect of peroxynitrite on glutaredoxin

Glutaredoxin is an important enzyme in thiol homeostasis. As a thioltransferase, it reduces oxidized thiols. It also has dehydroascorbate reductase (DHAR) activity to reduce dehydroascorbate (DHA) to ascorbic acid. Peroxynitrite (ONOO-) is one of the most active elements of oxidative stress that can be formed wherever nitric oxide and superoxide are produced simultaneously. ONOO- is known to react with free thiols easily. To observe the effect of ONOO- on glutaredoxin, rat liver cytosolic fractions were incubated with 0-250 muM ONOO-. Thioltransferase activity was found to be decreased as ONOO- concentration increased. The inhibition was not reversible with dithiothreitol (DTT). In cytosol besides glutaredoxin, another enzyme with DHAR activity is also present. In our study, the cytosolic DHAR activity which consisted both enzymes, was also inhibited by ONOO-, but DTT was able to return the activity almost completely.