SHAPE OF THE HEMOGLOBIN MOLECULE 



249 



layers which extend throughout the crystal. The molecule is thus 

 less asymmetric than was assumed, the ratio of the major to the 

 minor axis being 1.6. 



Perutz {2133) showed that by using the above dimensions for the 

 molecule, and the value of 0.34 for the hydration, much of the data 

 provided by other physical methods could be reconciled with his 

 structure. The value for the wet radius in solution is, within the 

 limits of experimental error, the same as that calculated by Poison 

 (2166) from the diffusion constant. Using the volume for the hydrated 

 protein, he showed that Poison's data {2167) for the viscosity of 

 solutions of hemoglobin no longer lead to a result in disagreement 

 with Einstein's equation. 



More recentlj' Oncley {2075) and Wyman and Ingalls {3137) have reviewed 

 the problems of the determination of the shape of protein molecules, taking 

 the correct values for the hj'dration into account. The following diagram 

 (Fig. 4), taken from Oncley 's paper illustrates the importance of the correct 

 estimate of hydration in arriving at the shape of the molecule. 



HYDRATION, grams water per gram protein 



Fig. 4. Values of axial ratios and hydration in accord with frictional ratios 

 (contour lines denote ///o values), according to Oncley {S075). 



