Spectra and Redox Potentials of Metalloporphyrins and Haemoproteins 57 



Table 2 



* From Lemberg and Falk, 1951. 

 t This study. 



Table 3 



Haems 

 Side chains in positions: 



£0 



of the (CN-)2 



derivatives* 



of the Pyridine2 

 derivatives! 



-CH2CH2COOH 

 -C2H5 



-CHOH— CH3 

 -CH=CH2 

 -CHO 



-CH2CH2COOH 

 -C2H5 



-CHOH— CH3 

 -CH=CH2 

 -CH=CH, 



-0-247 

 -0-229 

 -0-200 

 -0-183 

 -0-113 



-0-04 

 +0-107 



* From Martell and Calvin (1952). 

 t Vestling, 1940. 



Among those cytochromes b for which it has been estabhshed that the 

 prosthetic group is protohaem, there is again no correlation between spectrum 

 and redox potential; the same is true for those cytochromes c for which it 

 has been established that haem c is the prosthetic group (Morton, 1958). 



These anomalies can be due only to some particular properties of the 

 proteins. If we regard these biological compounds as further co-ordination 

 complexes of haems, to what extent can these differences from model com- 

 plexes be explained in terms of the nature of the protein-haem iron bonds ? 

 It is possible that, as ligands, the proteins may have properties difficult or 

 impossible to reproduce in model systems. Thus, the stereochemical environ- 

 ment of the protein ligand atom may influence the way in which this atom 

 co-ordinates. The protein, and in intact tissue perhaps other macromolecules, 



