THE KERATINIZATION PROCESS 219 



It seems not unlikely that other chemical modifications occur con- 

 comitantly. The changes in the affinity of the proteins in zones C, D and 

 E for acidic and basic dyes described by Auber (1950) Odland (1953) and 

 Montagna (1956) suggest that other side chain modifications are occurring. 

 According to Montagna's summary, the first-formed fibrils are basophilic, 

 i.e. they take up basic dyes in a pH range 4-6; as the material matures it 

 loses its power to bind basic dyes at lower pH values although it still binds 

 acid dyes. Evidently some acid groups are lost or modified. This could be 

 due to the conversion of some acid groups (COOH) to amides (CONH 2 ). 

 For example, in wool the effective acid and basic groups are closely 

 equivalent when allowance is made for the acids in amide form. Table 13 

 is adapted from Simmonds (1954 and 1955). 



Table 13. 



(gramme equivalents amino acids in 10 5 



g wool.) 



The amides may also contribute to the stability by participating in 

 hydrogen-bond formation. A more complete investigation aiming at the 

 localization of amino acid residues other than cysteine and cystine is 

 needed. Ryder has described preliminary tests for several (1959). Gillespie 

 et al. (1960) point out that analysis of the fibrillar (a-component, see p. 240) 

 and the y-component, which may enter during the progress of keratinization 

 (see p. 224), differ in their content of basic and acidic amino acids. The 

 matrix proteins (y-keratins) (p. 248) are more basic than the fibrillar 

 a-proteins. 



Nucleic Acids and Synthesis (Fig. 97 (b)) 



The dividing cells of the matrix (zone A) have prominent Feulgen- 

 positive nuclei and a basophilic cytoplasm containing RNA which is said 

 to increase as the cells differentiate (zone B) and commence to synthesize 

 protein. The pattern of the nucleic acids : well- developed DNA-containing 

 nuclei, prominent RNA nucleoli and a strongly RNA-positive cytoplasm 

 are compatible with current views of the role of these acids in synthesis as 

 outlined in a previous chapter. 



