ANIMAL COLLAGENASE AND COLLAGEN METABOLISM 



671 



I05 





^ 10^- 



^ 

 Q. 

 ^ 



10- 



10 



20 



HOURS AFTER PROLINE-H 



25 



30 



Fig. 4. Specific activit}- of the free proline in 1 m NaCl extracts of tail fin 

 and back skin. 



parent and probably reflects technical difficulties in making a com- 

 plete dissection because of the radical changes in body and head 

 shape. 



There was greater net incorporation of labeled proline in the back 

 skin collagen of metamorphosing animals than in the controls ( Fig. 

 5). In the tail fin, on the other hand, the reverse occurred. The spe- 

 cific activity of the back skin collagen was also higher, whereas there 

 was little difference in tail fin specific activities up to 20 hours 

 (Fig. 6). 



In the resting tadpole the amount of tail fin collagen was constant, 

 and there was a progressive increase in both total and specific radio- 

 activity over a period of 20 hours. The rates of synthesis and deg- 

 radation must be the same, but whether there is some selective 

 removal of old "cold" collagen or a nonselective random removal 



