ANIMAL COLLAGENASE AND COLLAGEN METABOLISM 



667 



TABLE I. Composition of Tail Fin and Back Skin in Thyroxin-Treated 



AND NONTREATED TaDPOLES" 



" Six days with 6 X 10~" m thyroxin in the water. 



* Fraction of extracted noncollagenous protein not precipitated by dialysis against 

 water. 



■ Metabolism of Collagen in Resting and 

 Metamorphosing Tadpoles 



The numerous studies conducted on turnover of the various col- 

 lagen fractions in mammalian tissues have provided a working 

 theory of collagen metabolism (Harkness et ah, 1954; Jackson and 

 Bentley, 1959; Piez and Likins, 1957; Hausmann and Neuman, 1961; 

 Prockop et al., 1962; Gould and Manner, 1962; Green and Lowther, 

 1959; Gross, 1959). The tropocollagen molecule (Gross et al, 1954; 

 Schmitt et al., 1955), synthesized within the fibroblast, is secreted 

 into the intercellular space and organized into fibrils. That fraction 

 which can be extracted in cold physiologic saline is considered to be 

 most recentlv synthesized, probabh' existing in the tissue as loose 

 molecular aggregates in fibrillar form. Probabh' the newlv secreted 

 collagen remains in the dispersed state for a very brief period in 

 most situations, since little collagen is extr actable at body tempera- 



