The Haem-Glohin Linkage 193 



Falk: It is clear that the basis of the difference which Perrin, Phillips and I have had 

 with O'Hagan is that he seems to consider the protein-haemoglobin bond as something 

 like a simple electrostatic bond, with virtually zero stability constant, where we 

 consider that co-ordination occurs to give a haem-giobin complex with a finite 

 stability constant. 



Regarding COO~ as the protein-iron bond in haemoglobin, my objection to this 

 is that of all the possible protein ligand groups, — COO" would tend to stabilize the 

 ferric state most. The stabilization of its ferrous state, compared to haem itself, is 

 perhaps the most important and the most outstanding special property of haemoglobin. 



