OXYHEMOGLOBIN IN DILUTE SOLUTIONS 



145 



and the exponent of the hydrogen-ion concentration is shown in 

 Fig. 45. 



The effect of temperature on the rate of the reaction 



HbO, 



Hb+ Og 



is also in strong contrast to its effect — or lack of effect — on the rate of 

 the reaction 



Hb + Oo 



HbO, 



Hartridge and Roughton made a series of measurements, both on 

 acid and alkahne solutions, and found that the velocity constant in 

 each case had the high temperature coefficient, 3-8. In the case of the 

 acid solution (pH = 5* 6) it was practicable to get measurements 

 only between 3° and 14° C, but in the case of the alkaline solution 



90 



60 



30 



-•• — a 



4 6 6 10 



Fig. 45. Abscissa = pHol solution. Ordinate = value of reduction velocity constant. 

 Squares represent results obtained in experiment on one sample of blood. 

 Circles represent results obtained in experiment on another sample of blood. 



(^H = 9), in which the reaction goes more slowly, data were obtain- 

 able up to 28° C. In both cases the observations which were made 

 inspire a good deal of confidence, since they fall into line with the 

 demands of Arrhenius' equation 



^1 /i/1 



log 



K2 R \^2 



^^j' 



according to which the logarithm of the velocity constant should 

 vary directly with the reciprocal of the absolute temperature. How 

 good the agreement is between the observed points and the theory 

 is shown by Fig. 46, B. 



Putting together the principal facts about the reduction and oxida- 

 tion velocities what fight may they be expected to shed on the 

 equilibrium curves of oxyhsemoglobin ? Three main points emerge. 



