264 



VI. HEMOGLOBIN 



Adair (c/. Section 4.1.) created great diflSculties for both the above 

 theories. While Hill's equation can describe the dissociation curve of 

 oxyhemoglobin if n == 2.5, it fails if n = 4. 



Adair overcame this difficulty (5) by pointing out that, if four 

 hemes were present in a molecule of hemoglobin, a number of species, 

 Hb4, Hb4(02), Hb4(02)2, Hb4(02)3, Hb4(02)4, could be present on oxy- 

 genation. The four hemes were not assumed independent, the affinity 

 of unoccupied hemes for oxygen being altered as the stepwise oxygena- 

 tion proceeded. 



Since we will frequently be referring to these intermediates, we 

 will describe them by the symbols : 



Hb, 



Hb4(02) 



Hb4(02)2 



Hb4(02)3 



Hb4(02)4 



It can be seen that the concentration of any one of these species can 

 be described by an equation such as: 



n° 



= K, 



D 



N 



The oxygen saturation is defined by: 



Z(02 present in all species) 



y 



whence : 



y = 



w (02-capacity of all species) 



Kjj) + 2 KiKzp^ + 3 KiKaKajo^ + 4 KiK2K3K4p^ 

 4 (1 + Kip + KiK2p2 + KiK2K3p^ + KiK2K3K47>^) 



It can be seen that Adair's hypothesis, while based on a more satis- 

 factory theory than the earlier hypotheses, introduces four constants, 

 making it even easier to fit a particular dissociation curve. Examples 

 of the ability of the equation to fit Hb02 dissociation data may be 

 found in the papers of Adair (5,6), Ferry and Green {7Jf7), and Forbes 

 and Koughton {918). 



Adair's hyjjothesis marked a considerable advance. His postulate 

 of the existence of intermediates gave rise to a number of attempts 

 to prove their existence by methods independent of Adair's equation. 



