GG4 r. M, LAPIERE AND J. GROSS 



The rapid removal of collagen which occurs during bone growth 

 and during retrogression of the postpartum uterus has stimulated 

 an intensive search for an animal collagenase operating under phvs- 

 iologic conditions (Morrione and Seifter, 1962; Woessner, 1962; 

 Rouiller, 1961). The many examinations of tissue extracts for col- 

 lagenolytic activity operating at physiologic pH and temperature 

 have uniformly been unsuccessful ( Mandl, 1961 ) . By culturing tis- 

 sues on reconstituted collagen gels we have recently demonstrated 

 the appearance of a collagenolytic enzyme in amphibian connective 

 tissues (Gross and Lapiere, 1962). Similarly, we have also detected 

 collagenolytic activity in rat uterine tissue and in bone. 



These studies have been extended and we wish to discuss the 

 results of simultaneous experiments on the metabolic turnover of 

 collagen and collagenolytic activity in resting and metamorphosing 

 bullfrog tadpoles. 



We have compared the collagen of the tail fin with that of back 

 skin since in the former complete removal occurs during metamor- 

 phosis, whereas in the latter there is increased production. 



Gross Changes in Tail Fin and Back Skin Connective 

 Tissue in Metamorphosis 



The dramatic remodeling of the frog tadpole in metamorphosis 

 has been amply described (Taylor and Kollros, 1946; Lynn and 

 Wachowski, 1951; Etkin, 1955; Kollros, 1961). There have been 

 several recent examinations of the detailed structural changes in 

 the body skin during metamorphosis (Kemp, 1959, 1961). Thus far, 

 however, there has been little quantitative chemical information 

 available on structural element modifications. We have examined 

 the alterations in the various collagen fractions, free proline, and 

 water and cellular content of both tail and back skin in order to 

 obtain information needed for studies on collagen turnover and 

 collagenolytic activity. Rana catesbiana tadpoles used in these stud- 

 ies were all at the same stage of development, either legless or with 

 hind legs less than 1 cm in length. 



Metamorphosis was induced by adding thyroxin in concentrations 

 of 10"^ M to the aquarium water. Control animals were starved, 



