188 J. E. O'Hagan 



3. With horse apomyoglobin nickel mesoporphyrin combines with a more 

 basic group or groups. 



4. Fresh evidence is presented that the group in apomyoglobin binding the 

 haem iron is more likely to be of the nature of a /J or y carboxyl than an 

 imidazole group. 



5. An interpretation of the sigmoid shape of the oxygen dissociation curve, 

 the Bohr effect, the alkaline stability, and the change of molecular shape on 

 oxygenation, in terms of labile electrostatic linkages between the haem 

 propionate groups and imidazolium side-chains of horse apohaemoglobin is 

 presented. 



6. It is suggested that the change in shape of the haemoglobin molecule on 

 oxygenation or reduction may 'agitate' the contents of the erythrocyte and 

 thus assists the exchange of oxygen and carbon dioxide between the cell 

 interior and the plasma surrounding its envelope. 



Acknowledgement 



Without the continued encouragement of Dr. A. E. Shaw and generous 

 provision of facilities by the Queensland Division of the Australian Red 

 Cross Society this work could not have been accomplished. 



ADDENDUM 



(Note added in proof) 

 The subsequent evidence of Kendrew, Dickerson, Strandberg, Hart, Davies, 

 Phillips and Shore (1960) indicates that the haem iron in myoglobin is 

 attached to imidazole nitrogen, not to a carboxyl group. Their work was 

 carried out with crystalline ferrimyoglobin, mine with this compound in 

 solution, but it is unlikely that the mode of attachment would be essentially 

 different in the crystal and in solution. 



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