ON THE NATURE OF HEMOPROTEIN REACTIONS 



tion of anion bonding comes from studies of the variation of the 

 equiUbrium constant for the fluoride reaction with ionic strength, 

 7(17). If log A' is plotted against v7 the slope of the line is — 1 .2 

 at low values of 7, compared to the theoretical slope of —1.0 

 expected for a reaction of the type 



Fe+(H20) + F- . FeF + H2O (3) 



where the change in charge on the iron is + 1 to zero. This 

 result also substantiates the structure assumed for the hemo- 

 protein with the iron joined to a neutral atom in an amino acid 

 residue, for if this atom were negatively charged the net charge 

 on the iron in the ferric state would be zero, and the charge 

 change in the above reaction would be from zero to — 1 . 



The pa changes which accompany the formation of ferri- 

 myoglobin fluoride and cyanide in unbuffered solutions, at 

 initial pH values of about 8 and about 1 0, were also what would 

 be expected if the anions were bound (16). 



Parallel studies of the pH variation of the velocity constants 

 for the formation and dissociation of the ferrimyoglobin cyanide 

 and fluoride complexes show that both complexes are formed 



TABLE II 



Reaction Mechanism and Provisional Kinetic Data for the Ferrimyoglobin- 

 Cyanide Reaction at 25°G. and I = 0.10 (16,18) 

 Symbols: H+Y Fe+CHjO) and Y Fe+CHjO) represent ferrimyoglobin with its 

 heme-linked group in the conjugate acid and base forms, respectively, the charge 

 being arbitrarily assigned to the former. 

 Units: 



ki, k[, ki, kj', k_i' and k_2', 1- mole"' sec."*: ^_i and k_z, sec."' 



ki = 3.7 X 10' 



k.i'= 1.0 X 10* 



fci = 1.6 X 106 



H +Y • Fe +(H20) + CN - . H +Y • FeCN + HjO (2) 



Ar-j = 7 X 10-" 



H+YFe+CHjO) + HCN , ' ° ^ H+Y FeCN + H3O+ (2') 



fc-i' = 4.5 X 10' 



347 



