JEFFRIES WYMAN, JR. 



400 and 4 for our rectangular model we should predict that completely 

 separating the haems of horse haemoglobin would lead to a decrease 

 of p h by a factor of 40. However, we are hardly justified in thinking 

 of myoglobin as a quadrant of a haemoglobin simply because the 

 molecular weight is one quarter, and too much cannot be argued from 

 this effect. 



The conclusions of this paper, based mainly on considerations relating 

 to the oxygen equilibrium of horse haemoglobin, but strengthened also 

 by data on other haemoglobins and by oxidation-reduction phenomena, 

 some of which have been mentioned and some not, may be stated as 

 follows. The four haems are all bound to structurally identical local 

 configurations of the globin, and each interacts with two acid groups, 

 one of which, the one active in the physiological range, is rendered 

 stronger, the other of which, the one active at more acid reactions, is 

 rendered weaker when an oxygen molecule combines. These groups 

 are probably imino groups of histidine. The four haems occur in pairs, 

 with strong stabilizing interactions between members of the same pair 

 and weaker interactions between members of different pairs. In the 

 oxygen equilibrium the interaction between members of different 

 pairs, amounting to about 800 cals, involves primarily the unoxygenated 

 haems and there is some indication that the same may be true of the 

 much stronger interaction (~3,500 cals) between members of the 

 same pair. 



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