238 KERATIN AND KERATINIZATION 



satisfactory owing to a marked polydispersity and a tendency to aggregate 

 with time. Mercer and Olofsson (1951b) reported 84,000; Woods (1952) 

 estimated for a low molecular weight diffusible fraction 10,000 and for the 

 non-diffusible 50,000. For a recent review see Gillespie et al. (1960). 



Jones and Mecham (1943) showed that many other keratins give soluble 

 extracts in solutions of urea containing reducing agents but with the 

 exception of feather (see below) little is known of the molecular character- 

 istics of the dissolved material. There is a marked resemblance between 

 these protein extracts and Rudall's epidermin. All precipitate as white, 

 sticky curds on the addition of ammonium sulphate and can be drawn into 

 fibres giving an a-type X-ray pattern. 



Very similar extracts were obtained from feathers by Lundgren, Ward 

 and associates (Ward et al, 1946; Ward and Lundgren, 1954). More 

 recently Woodin (p. 163) has claimed that better defined " monodis- 

 perse " derivatives can be obtained by careful reduction with thioglycollate 

 at pH 1 1 which would seem to prove that in the case of feather at least a 

 definite macromolecular monomer can be isolated. 



Oxidising reagents. Oxidation of the disulphide bonds with peracetic 

 acid was shown by Alexander and Earland (1950) to be an extremely 

 satisfactory method of obtaining a soluble derivative from keratins. The 

 oxidized keratin is readily soluble in dilute alkalis and can be thrown out 

 of solution on the addition of ammonium sulphate or acids as a white 

 coherent material, again resembling epidermin, which may be drawn into 

 threads yielding well-oriented a-type X-ray patterns. 



Not all of the material extracted from oxidized wool can be so readily 

 precipitated from solution. A portion remains and has been designated 

 y-keratose by Alexander (Alexander and Hudson, 1954). Ultracentrifugal 

 analysis shows that the solution of oxidized wool contains two somewhat 

 polydispersed components, but the physicochemical characteristics of 

 these are still in dispute (O'Donnell and Woods, 1955). This particular 

 method of dissolving keratins has provided nevertheless one of the most 

 valuable insights into the nature of keratinization. It suggested to Alex- 

 ander the existence in a hard keratin of two main components of very 

 different character : one fibrous of high molecular weight, the other non- 

 fibrous and of a lower molecular weight. This second fraction has the 

 much higher sulphur content (see Table 15). The insoluble fraction, 

 called /3-keratose (less than 10%) has been shown to consist principally of 

 the membranes of the keratinized cells (Mercer, 1951d and 1953), see 

 p. 260. 



Corfield, Robson and Skinner (1958) have determined the amino acid 

 composition of the oxidized keratin fractions (a, jS and y keratose) and their 

 results for a- and y-keratose are given in Table 16. 



It will be seen that y-keratose contains much larger amounts of cystine 



