The kinetics of hæmoglobin. III.—The velocity with which oxygen combines with reduced hæmoglobin

The velocity with which oxygen dissociates from its combination with hæmoglobin, and the factors upon which the velocity-constant of this reaction depends, have already been investigated by us in some detail in the second of the present series of papers (1). Since then we have been engaged in a similar inquiry into the velocity of the reverse reaction, i. e., the combination of oxygen with reduced hæmoglobin. The scope of the investigation, which we are now about to describe, was as follows:— (α) To determine the order of the reaction between oxygen and hæmoglobin (see p. 663). (β) To compare the value of the velocity-constant for the combination of O2 + Hb ______________________________________________________ the velocity-constant for the dissociation of O2 .Hb→ with the value of the equilibrium-constant of the reaction as determined from the dissociation curve. (γ) To study the effect of (i) pH (ii) temperature, (iii) light, and (iv) salt content upon the velocity of the reaction between O2 and hæmoglobin. The general methods adopted were similar to those used in studying the rate of dissociation of oxyhæmoglobin. One solution (I) consisted of water containing a considerable quantity of oxygen in solution, whereas the other solution (II) consisted of reduced hæmoglobin. These were driven by separate jets into the mixing chamber of the reaction velocity apparatus (2 and 3), and after mixing travelled steadily with known velocity down the observation tube. Spectroscopic observation of the ratio of oxyhæmoglobin to reduced hemoglobin concentration at various points of the tube, together with a knowledge of the rate of linear flow and of the total amount of (i) oxygen and (ii) hæmoglobin in unit volume of the mixed solution, gave us all the data required for the measurement of the velocity of the reaction.