FIGURE 2.

Observed rate constants at low NO are not due to NO bolus effect or nitrite contamination. A, comparison of observed rate constants from experiments with NO from either ProliNONOate or NO-saturated buffer. HbFe³⁺ (≈25 μm) was mixed with variable amounts of ProliNONOate or NO-saturated buffer to achieve the indicated NO concentrations. Reactions were performed at 37 °C in 100 mm sodium phosphate (pH 7.4). B, fast observed rate constants at low [NO] are not due to nitrite contamination of ProliNONOate. Methemoglobin (HbFe³⁺) solutions (23 μm) containing variable amounts of sodium nitrite were mixed with ProliNONOate to yield a final NO concentration of 5 μm. Reactions were carried out at 37 °C in 100 mm sodium phosphate (pH 7.4). The line is a linear fit of the data. C, high concentrations of nitrite do have an appreciable effect on observed rate constants at high NO. Methemoglobin (HbFe³⁺) solutions (30 μm) were mixed with 1 mm NO from ProliNONOate in the presence of a range of nitrite concentrations at 37 °C in 100 mm sodium phosphate (pH 7.4).