Cell and Solution Velocity Constants for the Reaction CO + Hb → COHb at Different Temperatures in Mammals with Different Red Cell Sizes

Using a double beam stopped-flow apparatus, measurements were made of the velocity constant of the reaction CO + Hb → COHb in solution and in the red cells of human beings, rabbits, horses, and goats. The solution constant (l') at 37°C for human beings was 362 mM^-1 sec.^-1; in other species l' was somewhat lower. Two rabbits, despite having apparently identical hemoglobins had significantly different values for l'. The energy of activation (E) of l' was between 8 and 11 kcal/mole in all cases. The cell reaction constant (l'_c) at 37° was between 61 and 73 mM^-1 sec.^-1 in all cases; at 37° the trend was for the smaller cells to have the higher l'_c. This cell size effect was much less than previously found for the faster oxygen reaction. This showed that by merely increasing the rate of chemical reaction, it was not possible to increase cell uptake rate beyond a certain level, this level being dependent on the size and membrane properties of the cell. At lower temperatures l' was a more important factor in determining l'_c than was cell size. The cell membrane was a barrier to gas diffusion in all species. The effect of temperature on l'_c was also measured and was less than its effect on l' at most temperatures. Temperature effect increased in small cells at low temperatures. Both these findings are in accordance with predictions based on differentiation of Roughton's equations.