INTERPRETATION OF KINETIC DATA 285 



Millikan used dithionite as an acceptor for oxygen. The combination of 

 oxygen with myohemoglohin, which is half complete in 0.4 millisecond, 

 proved to be the fastest reaction of this type so far discovered. As would be 

 expected, the dissociation of myocarboxyhemoglobin is sensitive to light. In 

 view of the insensitivity of the equilibrium between oxygen and myohemo- 

 glohin to pH changes, the finding that the rate of dissociation remained 

 unchanged between 7^H GM and pH 8.0 was not unexpected. In contra,st to 

 the hemoglobin reactions, the comparison of the Hiifner di.ssociation constant 

 with the ratio of the velocity con.stants for the forward and back reactions 

 is unexceptionable, since the dissociation curve may be described accurately 

 by the Hiifner equation. The data are summarized as follows for the system 

 at 20° C. and pH 7.4: 



The affinity constant, K = 9500. for the erjuilibrium: 



[MHbCQ] 

 [MHb] [CO] 



was not measured by Millikan, but was calculated from the affinity constant 

 he obtained by measurement of the oxygen equilibrium using Theorell's 

 {2762) value for the partition constant A' for the equilibrium: 



[ MHbOo] [CO ] 

 iMHbCO] [O2] 



Since the myohemoglohin reactions are adequately described by the 

 Hufner equation this procedure gives a correct value. 



6.3. Kinetics of Other Reactions 



Some data are available on the kinetics of other rapid reactions of hemo- 

 globin compounds. None of these have been investigated in the same detail 

 as the reactions with oxygen and carbon monoxide. The photoelectric reac- 

 tion meter has been used by Stern and DuBois (26.58) for the measurement 

 of the rate of reduction of hem?globin by dithionite (cf. also Chapter VII, 

 Section 11.3.). Roughton {2357) and Millikan {10'j2) have given data on 

 the reactions between ferricyanide and hemoglobin. Havemann {1188) has 

 analyzed the kinetics of the combination of cyanide with hemiglobin. 



7. INTERPRETATION OF KINETIC DATA 



7.1. Relation to Theories of Equilibrium 



7.1.1. Anomalous Support for Hiifner's Theory. In Sections 6.2.2. and 

 6.2.3., it has been pointed out that kinetic data exclude the earlier interpre- 

 tation of A. V. Hill's equilibrium equation, since p-fold variations of the 



