Reactions of heme proteins with carbonate radical anion

Reactions of radiolytically generated CO₃ ^•− with some ferric heme proteins, catalase, cytochrome c, and horseradish peroxidase (HRP), were studied. Carbonate radical anion oxidized amino acid residues of these proteins, but did not react directly with heme iron. HRP and catalase lost about 30% and 20% of their activity, respectively, after the reaction with 100 μM of CO₃ ^•−. The rate constants of the reactions of CO₃ ^•− with the investigated proteins measured by the pulse radiolysis method at pH 8–8.4 and 10 varied from 1.0 × 10⁸ M⁻¹ s⁻¹ (for cytochrome c) to 3.7 × 10⁹ M⁻¹ s⁻¹ (for catalase).