F. J. W. ROUGHTON, J. W. LEGGE and P. NICOLSON 



Until the Na 2 S 2 4 has reduced the dissolved 2 concentration to a low 

 enough value, the dissociation of 2 Hb in reaction (4.1) will be opposed 

 by the back reaction. On this theory, the lag period (at ph. 9-10, temp. 

 10-20°C) should certainly be over by the time the percentage O a Hb 

 has dropped to 90 per cent, for at this percentage saturation the maxi- 

 mum amount of oxygen which could exist in physical solution would 

 be very small compared with that in chemical combination (detailed 

 calculations are given by Roughton, 1949). Table I shows the calcu- 

 lated value of k for various saturation ranges in two recent experiments 

 on sheep haemoglobin solution at pH 10-0. It is clear that k does not 

 attain its constant plateau value until about one-third of the reaction 

 is completed. This point was missed by Hartridge and Roughton 2 , 

 because their method of observation was not available above 70 per cent 

 saturation. Some of Millikan's results show a similar trend to that of 

 Table /, but unfortunately he only recorded very few data in the upper 

 range. 



Table I 

 Relation of velocity constant, k, to range of saturation used for calculation 



Experiment A (13.3.47) 



pU 10-0, temperature 10-7°C. 

 Saturation 



range 87% to 71% OoHb 71% to 35% 35% to 20% 60% to 14% 

 Time in 



seconds 0-11 0-16 0-14 0-31 



Calculated 



value of k 1-8 4-5 4-0 4-7 



Experiment B (27.3.47) 



pR 10-0, temperature 16-8°C 

 Saturation 



range 85% to 68% 68% to 53% 53% to 3 1 % 31 % to 1 5% 



Time in 



seconds 0-07 0-035 0-048 0-07 



Calculated 



value of k 4-2 7-2 11-0 10-5 



Let us turn now to the kinetics of combination of CO with haemo- 

 globin. Re-examination of Roughton's data 7 shows that in some cases 

 the COHb concentration rises faster after the half-way stage has been 

 passed than would be expected on the basis of a constant value of k' 



70 



