Serum catalase as the protective agent against inactivation of alpha 1-proteinase inhibitor by hydrogen peroxide; comparison between normal and rheumatoid sera.

Human serum contains catalase activity, which can protect alpha 1-proteinase inhibitor from inactivation by H2O2. The primary source of serum catalase is probably erythrocytic. The enzyme activity correlates with haemoglobin concentration in sera from control subjects but not in sera from patients with rheumatoid arthritis. Catalase is inactivated by oxidants, such as H2O2 and hypochlorous acid and it is suggested that the decrease in catalase/haemoglobin ratio observed in rheumatoid serum is due to oxidant stress associated with inflammation.