O KERATIN AND KERATINIZATION 



sample after complete hydrolysis. In this way the familiar fibrous proteins, 

 collagens, keratins and silks were early shown to be distinct proteins, 

 characterized by the different amounts of amino acid residues forming 

 different patterns (Fig. 2). The common polysaccharides, cellulose and 

 chitin, yield glucose and acetoaminoglucose, respectively. 



There have been numerous analyses made of keratins beginning with 



==%- 



Alanine 

 Valine 



Leucine + isoleucir 

 Serine 

 Threonine 

 Phenylalanine 

 Tyrosine 

 Proline 



3 § Hydroxyproline 



Lysine 

 Arginine 

 Histidine 



Tryptophane 

 Aspartlc 

 Glutamic 



Amide N 



— - — i $ Cystlne/2 



Methionine 



Fig. 2. Number of amino acid residues in 10 5 g protein in three fibrous 

 proteins from Tristram's data (1953). 



(1) Silk fibroin (s) 



(2) Collagen (c) 



(3) Wool (w) 



§ Hydroxy-proline is only found in collagens and is regarded as " diag- 

 nostic." 

 If The cystine is given as " half cystine " (HS.CH.NH 2 COOH). 



