JEFFRIES WYMAN, JR. 



equation (3) depends only on /?H and not on Y (or y) so that we may 

 rewrite the equation as 



fbX\ d\ogp i 



[oYJpU dpH ....(3.1) 



By integrating this at constant pH we see that at any pH the number 

 of protons displaced as a result of oxygenation is proportional to the 

 degree of oxygenation.* That is, each successive molecule of oxygen 

 introduced into the haemoglobin molecule causes the same amount of 

 dissociation. This in turn means that each oxygen combining group 

 must be linked with an identical set of acid groups, identical at least 

 as regards their dissociation constants. Clearly in view of the double 

 character of the Bohr effect there must be at least two such groups 

 associated with each oxygen combining centre, one of which is rendered 

 stronger, the other weaker, as a result of oxygenation of the centre. 



Figure 1 . Values of log p± in 

 relation to pH for horse 

 haemoglobin at 25°C. 

 Smooth curve is calculated 

 from constants for oxygen 

 linked acid groups given in 

 Table I. 



10 



pH 



This interpretation may be checked in two ways. In the first place, 

 by direct differential acid base titration we obtain the difference of 

 charge between haemoglobin and oxyhaemoglobin. The data can be 

 satisfactorily fitted by the assumption of just two groups per haem, 

 the same for each haem, with the following choice of constants. 



Table I 



Apparent Dissociation Constants of Oxygen Linked 



Acid Groups in Horse Haemoglobin at 25° C and 



Ionic Strength 0-16 



pK x 

 pK 2 



Haemoglobin 

 7-93 

 5-25 



Oxyhaemoglobin 

 6-68 



5-75 



f (7iX\ dY 



— d log pi 

 dpH 



! 



dY = — dlogpi 

 dpH 



98 



