Figure 5.

pH dependence of the peroxynitrite isomerization rate constant in the absence of CO₂/HCO₃⁻/CO₃²⁻ (A), in the presence of 5.0 × 10⁻¹ M CO₂/HCO₃⁻/CO₃²⁻ (B), and in the presence of 3.0 × 10⁻² M CO₂/HCO₃⁻/CO₃²⁻ (C). In all three panels, the continuous lines correspond to k_obs, as defined in Equation (3), under different conditions (i.e., [L] = 0 (A), [L] = 5.0 × 10⁻¹ M (B), [L] = 3.0×10⁻² M (C), employing the parameters reported in Table 3. In (A,B), the open circles correspond to experimental data obtained from the literature [36] on the peroxynitrite isomerization rate constants as a function of pH under the conditions described above. The continuous lines were obtained according to Equation (3) by the non-linear least-squares fitting of data. In (C), the open circles correspond to values of k_obs in the presence of 3.0 × 10⁻⁵ M Dr-Nb(III) in the absence of CO₂/HCO₃⁻/CO₃²⁻ at different pH values (present study). Data shown in (C) indicate that, at pH 5.8, the efficiency of the heme protein (at the indicated concentration) is higher than that of the CO₂/HCO₃⁻/CO₃²⁻ system, while at pH 8.5, the efficiency is lower.