288 VI. HEMOGLOBIN 



technique used in the measurement of these reactions made it unlikely that 

 any of the less saturated intermediates were present, the reactions could 

 be expressed as: 



o' — lo o' — lo 



o' — 'o o' — 'o 



0| iCO Or |C0 



o' — Iq o' — I 



etc. 

 It has been shown above that if the dissociation of is allowed to 



o' 'o 



go to completion in the absence of carbon monoxide, the dissociation velocity 

 constant diminishes approximately sevenfold on changing from ptL b to 

 pH 8. Roughton explained the anomalous lacking of pH sensitivity of the 

 replacement reaction by assuming that the pH effect was only operative 

 when the less saturated intermediates were formed {2357), e.g.: 



n° '"■' Do 



7.3.2. Differences in Heats and Entropies of Reaction. In an interesting 

 contribution Eley {058) applies the transition state theory to the kinetics of 

 these reactions, and evaluates the entropies and heats of activation, AS* and 

 A//*, for these reactions and compares them with the over-all entropy and 

 heat changes, AS and A//, obtained from the equilibrium data. He points 

 out that the carbon monoxide reaction is "normal" and that the oxygen 

 reaction is "abnormal" in that the difference between ASg., and AS^is for 

 the forward and back reactions agrees within experimental error with AS 

 for the equilibrium in the former case, while in the latter there are very large 

 quantitative discrepancies. The position is similar with respect to the 

 differences between the heats of activation of the forward and back reactions 

 and for the equilibrium. The reader is referred to Eley's paper for discussion 

 of possible explanations for this peculiarity; Eley concludes that more data 

 are required on the rates of reaction of the partially saturated intermediates. 

 With respect to the actual velocities of the reactions, he points out that, 

 while similar heats of activation are found for the dissociation of Hb02 and 

 HbCO, the entropy of activation for the former is much larger than for the 

 latter. This may explain why the dissociation of oxyhemoglobin is much 

 faster than that of carboxyhemoglobin. The high velocities of the association 



