KERATIN AND MOLECULAR BIOLOGY 17 



a-keratins. Only two obvious spacings can be recognized corresponding 

 to the 10 A side spacing and the original 4-2 A halo, which here appears 

 with a dense and sharper inner circumference due to the presence of the 

 definitive 5-1 A spacing. 



040 



'331 



1 20 and 020 



'll2 



010 



9 • o • 



100 100 



etc. 



y 

 y 



Fig. 9. An early attempt by Astbury and Bell (1939) to indicate the 

 many other reflections visible in an a-pattern. The " indexing" (see Bunn, 

 1946) in terms of an orthorhombic cell: a = 27 A, b = 10-3 A, 

 c = 9-8 A, would not be accepted by all. See also Fig. 68, p. 166. 



(f) Disoriented ^-patterns (Fig. 11). Type example, boiled egg white. 

 The characteristic and often very sharp ring due to the 4-5 A backbone 

 spacing appears overlaid on the diffuse halo. The side-chain spacing 

 is sometimes less well defined. 



(g) Non-crystalline protein pattern. Many proteins when dried yield a 

 very vague pattern consisting of two diffuse haloes centred around 10 A 

 and 4-2 A which is distinguishable from the unoriented a- and /^-patterns 

 by the absence of either a 5-1 A or 4-5 A reflection. A close inspection 

 at the inner edge of the outer halo may be necessary to recognize the 

 absence of the a-spacing. 



It should be emphasized that these X-ray patterns are not indicative 

 of single specific proteins but of families of proteins which have in common 



