PROTEINS 



545 



secondary folding. The keratin primary valence chains are therefore 

 used by the animal body for the building of the horny tissues, either 

 heavily folded, or in more or less stretched condition. 



d. Connective Tissue {Collagen) 



Molecular structure of collagen and elastoidin. Tendons and decalcified 

 bones consist of the gelatinous protein collagen. Glue and gelatin are 

 relatively little changed decomposition products of this insoluble 

 frame substance which have become soluble in hot water owing to 

 sHght hydrolytic degradation. 



TABLE XXX 



CHEMICAL COMPOSITION OF COLLAGEN 

 (SCHAUENSTEIN AND STANKE, I951) 



Valine . . . 

 Leucine. . . 

 Proline . . . 

 Oxyproline . 

 Phenylalanine 

 Serine . . . 

 Threonine . 



/o 



2.8 



4-1 



12.7 



II. 2 



2.4 



5.0 



98.6 



Collagen is a protein the chemical composition of which differs 

 remarkably from the amino acid content of reserve proteins. It 

 contains a considerable amount of proline and oxyproHne (Table 

 XXX) but no tyrosine, tryptophane, cysteine nor methionine. 



Tendons and elongated gelatin both produce the same X-ray 

 pattern (Gerngross and Katz, 1926). It shows 8.4 A as the fibre 

 period which, divided among three amino acid residues, shows the 

 length of the members of the primary chain to be 2.8 A. Moreover, 

 there are two interferences on the equator of the diagram, which 

 correspond to 4.65 A (backbone thickness of the primary chain) and 

 10.0 A (length of the side chains). The resemblance to the conditions 

 in /5-keratin is striking, except that, as compared with the amino acid 

 residues of silk fibroin and of keratin, the primary chain period of 

 2.8 A would appear to be rather short. This may be due to the 



