Recent Developments in the X-Ray Study of Haemoglobin 



Figure 1 . Diagrammatic model of haemoglobin 

 molecule, showing its orientation with respect to 

 the crystal axes. Y is the diad axis. The small 

 disk underneath represents a haem group drawn 

 on the same scale and in the correct orientation 

 with respect to the crystal axes. The four lines 

 on the cylinder surface represent four layers of 

 scattering matter. {Reproduced from I.) 



Figure 2. Packing of haemoglobin 

 molecules in the crystal structure, show- 

 ing layers of close-packed molecules 

 separated by liquid. One unit cell is 

 shown in the foreground on the right. 

 (Reproduced from I.) 



The information derived in those studies is summarized in Figures 1 

 and 2 which show the shape of the haemoglobin molecules and their 

 arrangement in the lattice of the normal wet crystals. The haemoglobin 

 molecule is pictured in an idealized form as a cylinder of 57 A diameter 

 and 34 A height ; the four horizontal lines indicate four layers of 

 scattering matter whose presence was inferred from a one-dimensional 

 Fourier projection on to the cylinder axis. The small disk underneath 

 represents a haem group whose orientation relative to the crystal axes 

 can be found from the optical dichroism of the crystals (Perutz 5 and /). 

 Some indirect evidence regarding the positions of the haems on the 

 globin molecule will be discussed below. In the crystal the cylindrical 

 haemoglobin molecules are packed into layers which alternate with 

 layers of liquid. Within each layer every cylinder is surrounded by 



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