The Intermediate Compound Hypothesis 



from K 1 to <xK x , a being the ' interaction constant \ Similarly if an 2 

 molecule combines with a Fe atom adjacent to two Fe atoms already 

 combined the equilibrium constant is a?K x . 



2 Hb Per Cent 



vO-jp^optp^o ft o 



n-J J 



n-2-5 H 



r>*2 



Figure 2. Charts showing 

 agreement in per cent oxy- 

 haemoglobin between ob- 

 served data (Figure 1 and 

 Table I) and values calculated 

 from equations A, B, C, D, 

 E, F, G, H, J listed in text. 

 The zones of permissible dis- 

 crepancy are all 3 per cent 

 2 Hb deep, corresponding to 

 an experimental error of 

 ± 1-5 per cent 2 Hb. 



2 3 4 S 6 7 6 9 

 Oxygen Pressure in mm H<J 



Figure 2C shows that with K x = 0-0278 and a = 12, there is good 

 agreement over the middle of the curve, but serious failure at the top 

 and bottom. Decrease of a below 12 leads to better agreement at the 

 bottom, but only at the cost of worse disagreement at the top — vice 

 versa with increase of a. It seems therefore that Pauling's stimulating 

 theory must be abandoned. It was originally based on the more rugged 

 experimental data of R. M. Ferry and A. A. Green 6 . 



D G. S. Adair in an early paper on the intermediate compound 

 theory 7 put forward tentatively, and indeed mainly as an example, the 

 set of ratios of K x to K 2 to K 3 to AT 4 which form the basis of Figure 2D. 

 The actual values for the present data are 



K x = 0-359, K X K 2 = 0-0646, K X K 2 K 3 = 0-0155, K^K^ - 0-0167. 



There is considerable disagreement between the calculated and 

 observed data, especially in the upper half of the curve. 



E Ferry and Green 6 gave a set of ratios which they found very 

 satisfactory for describing their crystalline horse haemoglobin dis- 

 sociation curve data. If their ratios are applied to the data of Table I, 

 if is found that with 



^ = 0-28, i^o = 0-0251, ^/i: 2 ^3 = 000562, .M^A = 0-0166 

 there is good agreement except in the neighbourhood of 20 per cent 



87 



