236 KERATIN AND KERATINIZATION 



of the SH-positive zone dissolves which means that disulphide cross- 

 linking becomes effective at a rather definite point. Below this point 

 H-bonding is the major stabilizing element; above it is supplemented 

 progressively by disulphide cross-linking. The addition of reducing agents 

 (thioglycollic acid) to the urea carries the solution to a higher level. 



A velocity-sedimentation analysis of epidermin solutions in the ultra- 

 centrifuge was made by Mercer and Olofsson (1951a) and revealed the 

 presence of several components (three or more) with sedimentation 

 constants ranging from 1 to 7. These components were reduced to one by 

 the addition of a reducer which suggests that the heavier components 

 were aggregates of the lighter, held together by disulphide linkages. 

 Epidermin would seem to be a mixture containing some complexes already 

 united by disulphide bonds. 



Proteins have also been extracted from the follicle of the wool fibre using 

 the ingenious method of harvesting these in quantity devised by Ellis 

 (1948). Rogers (1959) has reported a detailed investigation on these 

 extracts and reached the conclusion that the larger part of the extract is a 

 fibrous material of low-sulphur content (< 2%) and that the remainder, 

 less well-defined, has the higher sulphur content ( >4%). A comparison 

 of the amino acid composition of whole wool and the fibrous low sulphur 

 component is given in Table 14 taken from Rogers. 



Soluble Derivatives of Keratinized Tissues 



This approach has attracted more attention for economic reasons. The 

 large quantities of keratinous materials going waste (hair, horns, feathers, 

 etc.) are a potential source of high molecular weight protein possibly of use 

 in the polymer industry (Jones and Mecham, 1943). 



On theoretical grounds one might look for a series of soluble derivatives 

 of definite molecular size ; in practice, solvents of little specificity must be 

 used and polydisperse mixtures, difficult to analyse, are obtained. Two 

 approaches to rupturing the disulphide bond are open : reduction or oxid- 

 ation. By using various different pH values and by adding hydrogen bond 

 breakers, a variety of products can be obtained. 



Reduction of wool. Sulphides which combine reducing properties with a 

 high pH have long been known as keratinolytic agents. Olofsson and 

 Gralen (1953) found that a sulphide extract of wool contained a mixture 

 of polypeptides of average weight of the order of 8000-10,000. Since all 

 disulphide bonds were broken, these polypeptides might be regarded as 

 primary although the high pH (11) may have produced some main chain 

 hydrolysis. Much earlier Goddard and Michaelis (1934 and 1935) used the 

 more specific reagent thioglycollic acid in alkaline solution, and obtained 

 solutions which contained two main components. 



Other methods of extraction make use of the simultaneous action of 



