ANIMAL COLLAGENASE AND COLLAGEN METABOLISM 661) 



the cold saline-extractable collagen might originate from degrada- 

 tion of nonextractable, previously deposited fibrils. 



Examination of the collagen fractions reveals marked differences 

 in distribution between back skin and tail fin, shov^n in Table II. 



TABLE II. Collagen (Hydroxyproline) Fractions in Tissues 

 OF Thyroxin-Treated and Nontreated Tadpoles" 



Av. total hydroxyproline 

 (/imoles per fin or back skin) 



Acid 



Wet weight Neutral extract 



per organ extract (0.1 M acetic 



(gm) (1 M NaCl) acid) Insoluble Total 



• " Average values for 140 whole fins and 140 back skins pooled and analyzed in 7 groups. 



In the former, cold neutral-extractable collagen accounts for only 

 3 per cent of the total, with the insoluble fibers accounting for 

 close to 70 per cent. In the tail fin there is a roughly equal distribu- 

 tion between the cold neutral-extractable, the acid-extractable, and 

 the insoluble fractions, the last accounting for onlv 26 per cent of 

 the total. There is a significant reduction in the proportion of in- 

 soluble collagen in the tail fin of thyroxin-treated animals, 17 per 

 cent as compared with 26 per cent in the controls. There is a coin- 

 cident rise in neutral-extractable collagen from 32 per cent to 43 per 

 cent. In the back skin, there is a proportionally smaller loss of in- 

 soluble collagen associated with a significant increase in the acid- 

 extractable fraction. 



A single dose of tritiated proline, 0.14 /xc per gm bodv weight, 

 was injected intraperitoneally into each tadpole. The thyroxin- 

 treated animals received the label at the same time as the controls. 



