202 



KERATIN* AM) KKRATIN I ZATION 



which had been released from the coiled-coil form of the normal a-structure 

 by the swelling and warming required to produce the pattern. If the 

 crystals are small and sufficiently disoriented, the two off-meridional spots 

 of the first row line (from the 54 A spacing) will spread and produce a 

 single arc across the meridian which will then appear meridional arising 



Fig. 86. Composite fibre diagram of X-ray reflections from Proteus 



vulgaris and Bacillus subtilis. The a-characteristics are indicated by 



reflection 47 and the cross-/? by 48. For the other spacings listed, see 



Astbury et al. (1955). Reproduced by permission. 



from a 4*7 A spacing. He likens the pattern to the completely-disoriented 

 halo pattern with spacings of 4-7 and 10-1 A (see p. 16) given by many 

 unoriented proteins. No trace of the 1-5 A spacing occurs in the X/3. 



Other a-proteins 



The a-proteins are among the commonest structural proteins to be 

 found both intra- and extra-cellularly. There is now no doubt that the 

 a-helix perhaps in a distorted form is to be found in the compact cor- 

 puscular molecules (Perutz, 1959). The significance of this would 



