ANIMAL COLLAGENASE AND COLLAGEN METABOLISM 



675 



10' 



- CONTROL 



\ M NaCI Extract 

 ■ — — ^ Insoluble 



Acid Extract 



THYROXIN Rx 



30 10 



HOURS AFTER H^Pro 



Fig. 7. Total activity of hydroxyproline isolated from the three collagen 

 fractions of tail fin. 



(Fig. 5) is due primarily to diminution in net incorporation in the 

 saline-extracted fraction. 



Looking at the specific activity relationships (Fig. 8), in the tail 

 fin we observe that the specific activity of the insoluble component 

 is greatly increased over that of the neutral-extractable fraction in 

 the resorbing tail, and is also much higher than that of the control 

 insoluble collagen. Similarly, while there is a fairly constant specific 

 activity in tlie acid-extractable component in the control, there is a 

 progressive increase in that of the other group. 



It would appear likely that the rise in specific activity, coupled 

 with a diminished amount of insoluble collagen, results from prefer- 

 ential removal of an unlabeled, hence older, portion of this pool, 

 indicating that the pool is metabolically inhomogeneous. Depression 

 of total and specific activity of the neutral-extractable fraction in 



