ON THE NATURE OF HEMOPROTEIN REACTIONS 



TABLE VII 

 Thermodynamic Data for Myoglobin and Hemoglobin Reactions at 25 °G. 



" Calculated from data given in references 34 and 43. 



>> Calculated from data in Table 6, reference 38, corrected by the appropriate 

 statistical factors. 



making the entry of successive oxygens easier (39). On this 

 basis, AS° for the first oxygenation should be more positive than 

 AS° for the last, and AH^ should be more favorable for the last 

 than the first. Neither do the data support another hypothesis — 

 that the interaction is between unoxygenated hemes, becoming 

 progressively less with increasing oxygenation (48), for on this 

 basis there should be no interaction affecting the entry of the 

 last oxygen, which should therefore resemble most the myo- 

 globin reaction. 



These new data for the hemoglobin reaction taken in con- 

 junction with those for myoglobin complexes, and particularly 

 the values of (^^l — ^m) suggest that an explanation for the 

 interaction can be sought in the following way. The value of 

 (-^ML — ^m) is "normal" for the entry of the first oxygen, 

 i.e., » +4 e.u., but is "abnormally" large and positive for the 

 entry of the last, i.e., ==s + 39 e.u. Interaction therefore sets in 

 after the first heme has reacted; it increases with increasing 

 oxygenation, in contrast with the predictions of the other hy- 

 pothesis just referred to. But the "normal" values of ("S^^l — 

 Sli) for myoglobin complexes, which range from —0.5 to 



365 



