ON THE NATURE OF HEMOPROTEIN REACTIONS 



basis, be even more positive than those for ferrous ion complexes, 

 and not some 30 e.u. more negative, as is actually found. The 

 comparison between (5^1 l "~ -^m) values for ferrimyoglobin 

 and cytochrome c and their cyanide complexes has shown how 

 the binding on heme in a crevice affects these values. A more 

 likely explanation in the case of hemoglobin and myoglobin is 

 the following. If the ferrous state, although neutral as regards 

 the net charge in the immediate vicinity of the iron atom, were 

 actually negatively charged over that part of the structure which 

 in its entirety determines the entropy change, then a negative 

 value for ('Spg(jj20) ~ ^e*(.moy) would follow because the 

 effective charge would increase and not decrease from +1 to 

 zero, as the ferric state is reduced to the ferrous state. This 

 criterion is satisfied if, for instance, the prosthetic group as a 

 whole with its negatively charged propionate side chains is 

 involved in determining the entropy changes, since the charge 

 change on reduction would then be —1 to —2. This inter- 

 pretation does not necessarily conflict with the conclusion drawn 

 from studies on the variation of equilibrium constants with 

 ionic strength, which showed that the iron in ferrimyoglobin 

 reacts between /?H 6.6 and 7.5 as if the charge were +1, provided 

 that this particular behavior is determined only by the resultant 

 charge on the iron atom. 



Aspects of the Bohr Effect and Heme-Heme Interaction 



These important physiological features of hemoglobin 

 reactions can now be examined in greater detail. The data for 

 the reactions of myoglobin, hemoglobin, and cytochrome c 

 discussed above show how the reactivity of these hemoproteins 

 and their affinity for ligands fit into a certain pattern. In some 

 respects it should therefore be possible now to distinguish a 

 "normal" reaction from one showing "abnormal" characteristics. 



With hemoglobin the magnitude of both of the interaction 

 effects depends, first, upon the source of the hemoglobin, 

 secondly, upon the treatment it has received, and thirdly, upon 



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