ERYTHROCYTES 



269 



Winkler and Bungenberg de Jong discuss this possibility; but, 

 iinding that the number of anionic COOH groups of the side chains 

 is not large enough for their tricomplex system, they place the main 

 chains perpendicular to the surface of the cell. 



Haemoglobin as a solute in close packing. Although the concentration 

 of haemoglobin reaches 34% in the red cell, it does not crystallize; 



Fig. 134. Close packing of haemoglobin in the erythrocyte (from Jung, 1950). t diameter, 



h height, d body diagonal of the haemoglobin molecule, a distance of molecular layers. 



The size of a hydrated Li + and K+ ion is given for comparison. 



it iills the erythrocyte as an isotropic solute. On the other hand, an 

 X-ray period of 62 A is furnished by living cells (Dervichian, 

 FouBusiET and Guinier, 1947). This period can be explained as follows 

 (Jung, 1950): The haemoglobin molecules are covered by a hydration 

 layer of 3 A, so that the dimensions of its thickset cylinder are 63 A 

 for the diameter /, 40 A for the height h and 74. 5 A for the body 

 diagonal d. If these molecules are allowed free rotation, every one 

 requires a spherical space of 74.5 A diameter (Fig. 134). Further, if 

 these spheres are arranged in hexagonal closest packing, a layer 

 distance of 61 A results, which is consistent with the X-ray period 

 found. Therefore, the state of the haemoglobin in the erythrocyte is 

 that of the densest solution possible, whose concentration has been 

 calculated to be 34*^0. 



It is evident that such an arrangement is most favourable for the 

 gas exchange of O, and COo. But why is it that such a saturated 



