The rate constants for Mb were obtained from analysis of simple pseudo–first-order conditions, at 37°C.^14,37  The T-state rate constants were derived from initial rates where all heme is in the T state.^14,22  The R-state rate constant for HbA₀ was obtained from modeling of the nitrite/hemoglobin reaction and from experimental data obtained at the end of the reaction when most Hb tetramer is in R conformation.^14,24  The R-state rate constant for solution-phase HbS was obtained by comparing the maximum rates for HbS and HbA²²  and estimating how much R-state and T-state Hb there is at this time point (which turned out to be 4% R state and 96% T state). We could not accurately estimate the rate constant for polymerized HbS since in experiments where this species was present we did not determine the concentration in the polymer phase. However, the data clearly showed that polymerized HbS reacts more slowly with nitrite than HbA₀, so that in the presence of HbS polymers, equation 3 would be modified as ^{−d[deoxyHb]/_dt}=[nitrite](k_R[R]+k_T[T]+k_p[P]), where P refers to deoxyhemes in molecules that are in the polymerized state. All bimolecular rate constants are measured or estimated at 37°C.