Recent Developments in the X-Ray Study of Haemoglobin 



chain direction (as nothing is known about the geometry of this pattern, 

 its existence is merely indicated by a series of lines normal to the chain 

 length), and a long-range zig-zag leading to distances of 10-5 A between 

 neighbouring portions of the same chain folded back on itself. In 

 (b) an arrangement of the chains has been chosen in which the two 

 prominent interchain vectors ' A ' and ' B ' are the most frequent. 

 The details in the two pictures are of course purely imaginative, but 

 the general layout which they indicate follows from the vector structure. 



Figure 8. Idealized picture of type of haemoglobin structure 

 compatible with Patterson synthesis, (a) Shows a basal section 

 through the cylindrical molecule with one polypeptide chain 

 folded in a plane, (b) Represents a vertical section through 

 the cylinder normal to X with the chains seen end on. 

 (Reproduced from II.) 



Discussion : The Positions of the Haems — In the following paper 

 Kendrew discusses the close resemblance between the basic structural 

 features of haemoglobin and myoglobin. X-ray studies of other 

 crystalline proteins indicate that the layered arrangement of the 

 polypeptide chains and their packing at distances of 10-1 1 A may be 

 frequently occurring features of globular protein structure. There 

 also appears to be a close connection between the polypeptide chain 

 structure in haemoglobin and that in the group of fibrous proteins 

 giving the well-known a-keratin pattern. This pattern generally 

 consists of only two reflexions, one at 5-1 A in the direction of the 

 fibre axis and another at 9-7 A at right angles to it (see for instance 

 plate 16 in W. T. Astbury 4 ). It seems that the 51 A reflexion in 

 a-keratin corresponds to the 5 A vector peak along the chain direction 

 found in haemoglobin. If we assume the chains in a-keratin to be 

 arranged in hexagonal close packing, the average distance between 

 neighbouring chains would be 9-7/sin 60° = 11 -2 A, which is the 

 same within the limits of definition of the vector peaks as the inter- 

 chain distance of 10-5 A found in the present analysis. This leads us 



143 



