The Intermediate Compound Hypothesis 



often in the past a particular theory of haemoglobin has been put 

 forward on the basis of data obtained under too restricted conditions. 

 It may, however, be noted that Forbes and Roughton 2 showed that 

 the curve of Figure 1, if the pressure scale was suitably adjusted, held 

 good over the pH range 7-3-9-3 (borate buffer) and for sheep haemo- 

 globin in distilled water (pH ca 8-2). It also agreed quite closely with 

 that of whole sheep blood at pH ca 8-1. Furthermore the recent data 

 of F. C. Courtice and C. G. Douglas 8 on whole human blood, in 

 presence of C0 2 , though they do not comply in several respects with 

 the conditions laid down at the beginning of this section, nevertheless 

 agree very closely with the sheep data except perhaps at the top of 

 the dissociation curve. 



AN INTERPRETATION OF THE KINETICS OF THE 



HAEMOGLOBIN REACTIONS ON THE BASIS OF THE 



INTERMEDIATE COMPOUND HYPOTHESIS 



This matter was considered in a preliminary way by Forbes and 

 Roughton 2 , Millikan 9 and in somewhat more detail by Roughton 11 

 On the intermediate compound hypothesis the kinetics of the chain of 

 four intermediate reactions may be formulated as follows : — 



Hb 4 + X ^ Hb 4 X l5 Hb 4 X x + X ^ Hb 4 X 2 , etc 



K\ /C 2 



where k x \ k 2 ' etc are the velocity constants of the four combination 

 reactions 

 k u k 2 etc are the velocity constants of the four dissociation 

 reactions 

 and [Hb 4 ] = C , [Hb^] = C ls [Hb 4 X 2 ] = C 2 etc 



C = total concentration of various haemoglobin compounds 



= c + q + c a + c 3 + c 4 



y = percentage saturation 



p = partial pressure of dissolved X (either 2 or CO). 



Then [XHb] = ^ = C x + 2C 2 + 3C 3 + 4C 4 



and [Hb] = 4C (1 5^ = 4C + 3C X + 2C 2 + C 3 



On this basis the velocity of the n ,h intermediate reaction 



= kffpC^^knC,, 



In the case of the dissociation of 2 Hb in presence of Na 2 S 2 4 , 

 the concentration of X remains zero, and the back reaction velocity 



89 



