PHILIP GEORGE 



by two distinct reaction paths, one with the undissociated acid, 

 and the other with the anion (17,18). The reaction mechanism 

 is set out for the case of the cyanide complex in Table II. A 

 consistent analysis of results is possible on the basis that the 

 reactions of alkaline ferrimyoglobin, YFeOH, in which a proton 

 has ionized from the water molecule coordinated to the iron, are 

 negligible in the comparison with the other four reactions, 1, 1', 

 2, and 1' . The various forward and back velocity constants, 

 k^ and k-x, etc., have been calculated from the experimentally 

 determined velocity constants for the formation and dissociation 

 of the complex, kj and k^, and the over-all equilibrium constant, 

 iTobs using the equations : 



"^ ~ {Kr + H+)(^HCN + H+)(^Fe + H+) 



k, = ^^ _^^^^ {^,(^-1 + r_:H+) + H+(A;_2 + k'^,U+)] 



and 



TT — f 



Aobs. — ~r 



Kr X {K, + H+) X H+ X ^HCN 



X 



m 



" {Kr + H+) X ^, X {Kjr. + H+) X (A^HCN + H+) 



Kr and K^, are, respectively, the ionization constants for the 

 heme-linked group in ferrimyoglobin and the complex, ^hcn 

 and K-pe are the ionization constants of HCN and of the co- 

 ordinated water molecule in acidic ferrimyoglobin. In the 

 analysis it is not possible to distinguish between reactions \' 

 and 2, i.e., YFe+(H20) + HCN and H+YFe+CHsO) + CN" 

 because both reactions show an identical j&H variation in the j&H 

 range of the experiments. It has been assumed that each path 

 contributes equally in order to calculate the velocity constants 

 k[, k_[, ki, and k-^, which are listed in Table II along with 

 those for reactions 1 and 2'. These values are provisional 

 because a more detailed investigation over the entire pH range 



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