H. E. DAVENPORT 



pU 9 is double that at /?H 6. R. M. Ferry and A. A. Green 8 have 

 reported a reversal of the Bohr effect in mammalian bloods below 

 pYL 6-5 but no kinetic studies upon this phenomenon have been 

 published. 



Temperature change has a marked influence upon the reaction 

 velocity. In a series of measurements between 4°C and 20°C a 

 twentyfold increase in the reaction velocity was found to occur. The 

 temperature effect follows the Arrhenius equation and has a tem- 

 perature coefficient of 5 compared with 3-8 for sheep haemoglobin 4 . 

 Extrapolation of the data to 38 °C, the normal temperature of the 

 environment of Ascaris gives t 50 = 10 sec, a value far greater than 

 the 0-0025 sec deduced by Hartridge and Roughton for sheep haemo- 

 globin at mammalian body temperature. 



The results so far described diverge widely in the magnitude of the 

 time scale from those obtained with other haemoglobins but their 

 validity was confirmed by a further series of experiments. According 

 to J. B. Conant 9 ferricyanide in presence of oxyhaemoglobin reacts 

 only with dissociated haemoglobin. G. A. Millikan 6 has used 

 ferricyanide as a means of immobilising dissociated haemoglobin in 

 his measurements of the dissociation velocity of muscle CO-haemo- 

 globin. When ferricyanide replaced sodium hyposulphite in experi- 

 ments with the Ascaris oxyhaemoglobins it was found that t 50 was 

 the same for both reactions. Control experiments showed that 

 variations in the ferricyanide concentration had no effect upon the 

 reaction velocity and that the magnitude of the back reaction of 

 dissociated haemoglobin with liberated oxygen was insignificant. 



Slow reactions of this kind are not without precedent in the gas 

 relations of other haemoglobins. It was shown by Roughton 10 that 

 the velocity constant for the dissociation of CO from sheep haemo- 

 globin at pH 7 and 20°C is 0-044. By a coincidence this is also the 

 value for the oxygen dissociation velocity constant of Ascaris perienteric 

 fluid haemoglobin under the same conditions. 



Carbon monoxide displaces oxygen very slowly from combination 

 with the Ascaris haemoglobins. The spectra of the CO-haemoglobins 

 (Figure 2) were measured in presence of Na 2 S 2 4 since rapid reversion 

 to oxyhaemoglobin occurs if traces of oxygen are present. The CO- 

 affinity of the haemoglobins is thus relatively low. Roughton 10 has 

 shown that oxygen dissociates from sheep haemoglobin 10,000 times 

 faster than CO but associates only 30 times more rapidly. The great 

 relative affinity for CO, 250 times the affinity for oxygen, is thus 

 principally the result of the low CO dissociation velocity. Using the 

 ferricyanide method it was found that CO dissociates from the Ascaris 

 haemoglobins more rapidly than 2 . With body wall haemoglobin, 



298 



