282 VI. HEMOGLOBIN 



and others will be present and there is no guarantee that the dissociation of 

 molecules of carbon monoxide from such hybrid ferrous-ferric compounds can 

 be directly compared with the dissociation from entirely ferrous compounds, 

 such as: 



C0| 1 COr 



co' — 'CO col 



Roughton removed the hemoglobin from the system by combining it with 

 oxygen. Since a similar objection could be raised to this procedure, involving 

 as it did the dissociation of molecules of carbon monoxide from hybrid 

 carboxy-oxyhemoglobins of the structures: 



COj lO COj lO 



co' — ' co' — 'o 



he pointed out that the velocities measured under these conditions referred 

 only to the rate of dissociation of the first of the four carbon monoxide 

 molecules and that the results were not comparable with those obtained 

 when the dissociation of oxyhemoglobin was measured with the aid of 

 dithionite. 



6.2.5. CO + Hb02 -^ HbCO + O2. This reaction had been the 

 first which Hartridge and Roughton had measured with their flow 

 technique {11^6). They found certain anomalies to be present in their 

 earlier work and the reaction was reinvestigated by Roughton in 1934 

 {2357). The rate of appearance of carboxyhemoglobin is described 

 by the equation: 



d[YihCO]/dt = k jHb02][CQ ] _ ^^ j-^^^Qj 



On account of slow dissociation of carboxyhemoglobin the back 

 reaction is neglected. Roughton initially kept the partial pressure 

 of oxygen constant and varied the concentrations of carbon monoxide 

 and oxyhemoglobin. The value of k2 remained unaltered when the 

 concentrations of carbon monoxide and oxyhemoglobin were varied 

 22-fold, [O2] remaining constant. This was found to be the case 

 between pH 6 and pH 10 and between temperatures from 11° C. to 

 21° C. By keeping the concentrations of carbon monoxide and 

 oxyhemoglobin constant, the reaction velocity varied inversely with 

 the concentrations of oxygen when the latter was varied sixfold. The 

 effect of temperature on the reaction was not thoroughly investigated 



