ANIMAL COLLAGENASE AND COLLAGEN METABOLISM 691 



the lytic cells, i.e., they carry the enzyme to its substrate. It seemed 

 unlikely that storage of the active enzyme in the tissue occurred. 

 Its accumulation in culture appeared to be a result of new synthesis 

 or activation of a zvmogen molecule. 



By growing large amounts of tadpole tail fin in petri dishes on 

 filter paper in Tyrode solution, coUagenase could be harvested from 

 the culture medium. Partially purified tadpole collagenase had a pH 

 optimum between 6.5 and 7.8, was destroyed bv heating between 

 50 and 60 °C for 10 minutes, and was reversibly inhibited by EDTA. 



A small but definite amount of reconstituted collagen fibrils was 

 digested by very high concentrations of trypsin, chymotrypsin, pa- 

 pain, elastase, and pronase. Unlike that of collagenase, the action of 

 other proteolytic enzymes was not progressive with time but was 

 complete within 1 to 2 hours; and considerably larger amounts of 

 enzyme were required for detection of this minimal activity. Both 

 bacterial and tadpole collagenase showed complete reversible in- 

 hibition by low concentrations of EDTA, whereas the other proteases 

 were only slightly affected. 



It seems likely that the cells responsible for the reorganization of 

 the tissues in different regions respond differently to thyroid hor- 

 mone. Perhaps in the loci where very intricate remodeling takes 

 place, as in the mouth parts, the differential response to thyroid 

 hormone in highly localized regions plays a key role. 



Acknowledgments. This work was supported by United States Public 

 Health Service Grant AM-05142-02. 



Publication No. 342 of the Robert W. Lovett Memorial Group for the 

 Study of Diseases Causing Deformities, Harvard Medical School at the 

 Massachusetts General Hospital, Boston, Massachusetts. 



Refer ENCE.S 



Allen, B. M. 1929. The influence of the thyroid gland and hypophysis upon 

 growth and development of amphibian larvae. Quart. Rev. Biol, 4, 

 325-352. 



Clausen, H. J. 1930. Rate of histolysis of anuran tail fin and muscle during 

 metamorphosis. Biol. Bull, 59, 199-210. 



Etkin, W. 1955. Metamorphosis. In Analysis of Development (B. H. Wil- 



