Decomposition of H₂O₂ by haemin. Inhibition of the reaction by azide

1. 1. NaN₃ inhibits the haemin-catalysed decomposition of H₂O₂. The inhibition is of the competitive type. Haemin itself does not combine with azide. 2. 2. The results are in agreement with a mechanism in which the formation of two intermediate complexes between haemin and H₂O₂ is assumed. Inhibition occurs by a reversible combination of azide with the secondary haemin-H₂O₂ complex. 3. 3. The inhibition is not complete. The catalyst-substrate-inhibitor complex still possesses some residual activity. 4. 4. Increased affinity for azide in the presence of H₂O₂ has also been observed in catalase. The analogous behavior towards azide may indicate a basic similarity of the catalytic mechanism in the two systems.