F. J. W. ROUGHTON 



k finally reaches the same plateau value of 1-0 but not till y has fallen 

 to 60 per cent. For k x = 3, the plateau value of k = 1 is reached only 

 at y = 30 per cent. For k x = 0-25, k = 0-25 throughout, i.e. the 

 reaction is again kinetically unimolecular from start to finish but the 

 rate is exactly a quarter of that with k 1 -^ co . 



To comply with the experimental finding that k reaches a plateau 

 value of 12 at and below about y = 70 per cent, it therefore appears 

 that ki must be set equal to 12, and k x to a value between 9 x 12, 

 i.e. 108, and 5 X 12, i.e. 60. 



Since K A = 8-8 and k A '/k t = K 4 , it follows that k\ = 12 x 8-8 

 = 106. The value of k\, which was previously indeterminate is thus 

 now fixed. 



Since K x = k x \k x 



therefore k x = -J- = — — - = 75 



K x 0-32 



= 150 



k 2 ' _ 18 



K 2 | of 0-32 

 kl = 12 

 K z \ of 0-32 

 k 2 ' = 18) k 3 ' = 12) k A ' == 1061 



k — 3 — 



* 3 ~ ^ " I^f032 ~ 22!> 



[ it is thus 

 150) k z == 225J k A = 12) 



possible to account quantitatively (a) for the equilibrium between 2 

 and sheep haemoglobin at alkaline pH (b) for the kinetics of combina- 

 tion and dissociation over the range where the equation d[XHb]/dt 

 = &'[A"][Hb] - &[XHb] holds good, and semi-quantitatively for (c) the 

 divergence of the data from the latter equation when [XHb] is high. 

 It is interesting to see that, on the present view, the large interaction 

 in the last intermediate reaction is due, in almost equal measure, to 

 the respective degrees to which k 4 ' and k A are affected, for the former 

 is increased to 106/6, i.e. 18 times the statistical value, and the latter 

 is decreased to 12/300, i.e. 1/25 of the statistical value. 



The work just described constitutes, I believe, the first thorough- 

 going attempt to treat both the kinetics and equilibria of haemoglobin 

 on the basis of the intermediate compound hypothesis, albeit on the 

 assumption of one particular form of the latter. Although successful 

 so far, final judgment as to the status of the work must be reserved 

 until its application has been tested in regard to other types of data 

 than those for which it has so far been used. Several previous theories 

 of the haemoglobin equilibria have, as has been pointed out above, 

 worked quite well until they were applied in directions for which they 

 were not originally designed : and it must be admitted that the basal 



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