LINKAGE IN HEMIGLOBIN 237 



behavior. A certain simplification was introduced in this scheme by 

 assuming that pK2 of 6.65 in the hem/globin represented the same 

 group which shifts from the pK^ of 7.8 in hemoglobin to a pK2 of 6.8 

 in oxyhemoglobin. Wyman and Ingalls {3136) showed that this was 



TABLE III 



Heme-Linked Acid Groups" in pYi. range 4.5 to 9* 



Group pKi pKi pK.3 



Hi+ 5.3 Mo \ 6.65 Si, Mi, Po 8.10 So, Mo \ 



Hb 5.25 Mi / 7.81 Si, Mi j 



HbOj 5.75 Mi, Po 6.80 Si, Mi, Po 



" S, M, and P refer to spectrophotfunetric, magnetometric, and polentiometric measure- 

 ment, respectively; o or i indicate whether the particidar />K has })een found 

 operative or inoperative by the particular technique employed. 



* -According to Coryell and Pauling (Ii99). 



probably the case, since they were able to describe adequately the 

 difference between the base bound by hemzglobin and by oxyhemo- 

 globin solely in terms of the pKs group in hemoglobin, to which they 

 assign the value 8.05. 



By an ingenious treatment (cf. Section 5.2.4.) of the data of Taylor 

 and Hasting for the Eh of the hemoglobin ;=± hemiglobin oxidation- 

 reduction system and of the results of Ferry and Green (7^7) for 

 the oxyhemoglobin ;=^ hemoglobin equilibrium, Wyman and Ingalls 

 arrived at the following pK values for these systems at 25° C. and ionic 

 strength 0.16: 



Henie-Iinked acid groups 



where ;;Ki and pKo represent the ionization of the distal and proximal 

 imidazole groups, respectively (Section 3.2.2.2.), and pKs, the disso- 

 ciation of the hematin. The above pK values were not derived from 

 the data of one experimental approach only, but represent tho.se 

 values which provide the best fit of the above data as well as the 

 values they obtained from data on the differential titration systems. 

 The way in which they did this is di.«cussed in Section 5.2.5. 



Coryell and Pauling (499) treat the behavior of the hematin-linked 



