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C. M. LAPIERE AND J. GROSS 



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1 2 3 4 5 6 7 

 DAYS AFTER THYROXIN 



Fig. 13. Collagenolytic activity of tadpole tail fin and back skin, and de- 

 crease in tail length, as functions of time of exposure to thyroxin. 



increase in enzyme activity with loss in tail length is clear; the ac- 

 tivity of the back skin shows no relation to the change in tail size. 



Isolation and purification of the tadpole collagenase from mass 

 cultures was made possible by the development of two sensitive 

 assay techniques which detect as little as 0.01 />tg of bacterial col- 

 lagenase. The first assay depends upon the release of radioactive 

 peptides from radioactive collagen, the released fragments being 

 measured aftei incubation ( Lapiere et al., submitted for publica- 

 tion). The second method is based upon decreased collagen fibril 

 formation after incubation of a reaction mixture containing the en- 

 zyme preparation and dissolved collagen at 25 °C. The temperature 

 is then elevated to 37 °C, polymerization of the collagen to an opales- 

 cent gel occurring in a few minutes. The reduction in opacity is a 

 direct measure of collagenolytic activity (Nagai et al., unpublished 

 observations ) . By growing large amounts of tadpole tail fin in petri 



