6 J. C. KENDREW 



of the polypeptide chain (the secondary structure), we find simphcity and 

 regularity once more. This regularity was first appreciated by Astbury in 

 his classical studies of fibrous proteins, resulting in his classification of 

 polypeptide chain configurations into three main types, to one of which 

 almost all known fibrous proteins conform. The most important of these 

 is the so-called a-configuration, and its structural basis was revealed by 



Fig. I. Model of myoglobin based on the three-dimensional Fourier syn- 

 thesis at a resolution of 6 A, showing the general arrangement of the polypeptide 

 chain and the position of the haem group. 



Pauling and Corey [i] when they discovered the a-helix. For some time 

 indirect evidence has been accumulating that the a-helix is a structural 

 element in the globular as well as in the fibrous proteins, but definite 

 proof of this has only recently been obtained, in the structure analysis of 

 myoglobin. 



The first stage of the X-ray analysis of myoglobin [2] gave a three- 

 dimensional picture of the molecule at a resolution of 6 A (Fig. i), reveal- 

 ing the general arrangement of the polypeptide chain and of the haem 



