FIGURE 2.
Apparent bimolecular binding rate constants for NO uptake by phospholipid vesicles under anaerobic conditions. A, the apparent bimolecular rate constant (y axis, logarithmic scale) plotted versus intracellular Hb concentration for a vesicle with a diameter of 250 nm. Our simulations, which included physiological values of NO diffusion outside (Dex), diffusion of NO and Hb inside (Din), and membrane permeability of NO (Pm) are shown as black circles. The multiplication factor of 1 used in the legend indicates that these parameters retained physiological values presented in Table 1. The simulated rate constants of Sakai et al. (21) are displayed as white circles and their experimentally measured rate constants are shown as gray diamonds. The rate constant for NO binding by a solution of free deoxygenated Hb is shown with the white square on the y axis. B, our simulated rate constants plotted versus intracellular Hb concentration for a vesicle of 250 nm in diameter when all parameters had physiological values (black circles, the same data as in panel A), when only the diffusion rate of NO outside a vesicle had a physiological value, whereas the other parameters were effectively infinite (gray triangles), when only the diffusion rate inside (of both NO and Hb) had a physiological value (white circles) and when only membrane permeability of NO had a physiological value (gray squares). For each set of simulations, the parameter that was assigned its physiological value presented in Table 1 is indicated with a multiplication factor of 1 in the legend. The parameters that were assigned effectively infinite values (Table 1) are indicated with a multiplication factor of infinity in the legend. For example, 1 × Pm refers to the physiological phospholipid membrane permeability of 9 × 105 μm s−1 and ∞ × (Dex, Din) indicates the very high diffusion rate constants of 33 × 108 μm2 s−1 for both diffusion of NO outside (Dex) and diffusion of NO and Hb inside (Din). C, rate constants analogous to those of panel A, but plotted versus vesicle diameter at an intracellular Hb concentration of 21.7 mm. D, rate constants analogous to those of panel B, but plotted versus vesicle diameter at an intracellular Hb concentration of 21.7 mm.