274 VI. HEMOGLOBIN 



unable to find a significant difference between these two cases, due, 

 perhaps to the rapid estabHshment of equihbrium, or to the experi- 

 mental difficulties. 



5.2.3. Complex Oxidation-Reduction Systems. In Chapter V we have 

 discussed the relations between the oxidation-reduction potential of the 

 hemochromes and the relative affinity of the base for heme and hematin. 

 As a by-product of their investigations into the reversibility of the hemoglobin- 

 hem/globin system, Conant and Scott (Jf78,Jf.79) have dealt with the analogous 

 effect that combination between oxygen or carbon monoxide and hemoglobin 

 has on the oxidation-reduction potential. Conant treats the problem in the 

 following way {4-71), which is similar to the more elaborate treatment 

 accorded by W. M. Clark to the hemochrome systems {cf. Chapter II). 



In the presence of the gas (oxygen or carbon monoxide) at partial pressure 

 X, the saturation, y, is defined by the equation: 



ij.= [Hb02]/[Hb02 + Hb] 



and the fraction not combined with the gas, and therefore to be considered 

 in the electrode equation, is equal to (1 — y). The electrode equation at 30°C. : 



„ „,, 0.0601, /[Hi+]\ 



becomes, in the presence of the gas at partial pressure x: 

 ^ -^- 0.0601 , [Hi+] 



E:c = E^ + log 



(1-y) [Hb02 + Hb] 

 When [Hi+] = [Hb02 -|- Hb], the equation becomes: 



n \1 - y/ 



Now, the Hill equation (Section 5.1.3.) may be cast into the form 

 log ( ) = log K — n' log X, where y and x are defined above, K is 



C-') 



the reciprocal of the dissociation constant used in Section 5.1.3., and n' is 

 the sigmoid coefficient, which is written with a prime to distinguish it from 

 the constant n in the electrode equation. 



If the ferrous form of the pigment is almost completely saturated with the 



gas, log ( I becomes nearly equal to log (1 — y),'m which case the error 



\ y J 



is small in writing: 



log (l — y) = log K — n' log x 



