Modification oj the Secondary Structure of Haemoprotein Molecules 93 



values, or of the difference of affinity for haem of nitrogen bases of the 

 unfolded cytochrome c molecule at different pH's. It was found also that the 

 number of haem-binding groups of cytochrome c decreased when the molecule 



Haem added, xiQ M 



Fig. 12. Effect of acetylation of the cytochrome c molecule on its affinity for 

 haem. Cytochrome c concentration, 3-3 X 10~* M. I, non-acetylated; II, 25% 

 acetylated; III, 80% acetylated; IV, 89% acetylated. The reaction was carried 

 out at pH 13-2. Percentages of acetylated amino groups of cytochrome c were 

 estimated by the DNP-method. The broken line indicates the concentration 

 curve of alkali-denatured globin haemochrome. 



was acetylated as shown in Fig. 12, The data suggest that chemical groups of 

 cytochrome c which bind with added haem may be e-amino groups of lysine. 



SUMMARY 



It was shown that the haem-haem interaction, the Bohr effect and the 

 affinity for ethyl isocyanide of haemoglobin were independent of each other 

 and were affected in different ways by urea. 



The addition of various carboxylic acid salts and detergents to haemoglobin 

 and cytochrome c caused modification of the secondary protein structure 

 and alteration of the proper functioning of the haemoproteins. These changes 

 were shown to proceed stepwise. 



The affinity of basic amino acids for haem appeared to increase when the 

 acids were integrated into larger peptide molecules. 



These studies provide evidence of the importance of the secondary structure 

 of the protein moieties of haemoproteins for their specific functions. 



