Studies on the Equilibria and Kinetics of the Reactions of Peroxidases with Ligands. III. The Dissociation of Carbon Monoxide from Carbon Monoxide FerroHorseradish Peroxidase

Carbon monoxide ferrous horseradish peroxidase dissociates very slowly in a reaction which exhibits firstorder kinetics. The rate was measured by trapping the liberated ferroperoxidase with either oxygen, in which case ferric peroxidase was the product, or with nitric oxide. The rate increases with increasing pH. The heat of activation was found to be approximately 30 kcal/mole. The dissociation velocity constant (L) at 30° and pH 7.00, using NO as a trapping agent, has a value of 1.1 ± 10⁻⁴ sec ⁻¹, corresponding to a halftime of about 2 hr. The dissociation velocity constant at 20°, estimated from this value and the heat of activation, is 1.6 μ 10⁻⁵ sec ⁻¹.