Oxidation of Carbon Monoxide by Perferrylmyoglobin

Abstract

Perferrylmyoglobin is found to oxidize CO in aerobic aqueous solution to CO₂. Tryptophan hydroperoxide in the presence of tetra­(4-sulfonatophenyl)-porphyrinate-iron­(III) or simple iron­(II)/(III) salts shows similar reactivity against CO. The oxidation of CO is for tryptophan hydroperoxide concluded to depend on the formation of alkoxyl radicals by reductive cleavage by iron­(II) or on the formation of peroxyl radicals by oxidative cleavage by iron­(III). During oxidation of CO, the tryptophan peroxyl radical was depleted with a rate constant of 0.26 ± 0.01 s^–1 for CO-saturated aqueous solution of pH 7.4 at 25 °C without concomitant reduction of the iron­(IV) center. Carbon monoxide is as a natural metabolite accordingly capable of scavenging tryptophan radicals in myoglobin activated by peroxides with a second-order rate constant of (3.3 ± 0.6) × 10² L mol^–1 s^–1, a reaction that might be of importance in cellular membranes of the intestine for protection of tissue against radical damage during meat digestion