INTERACTION OF COLLAGEN MACROMOLECULES 41 



action properties of TC resulting from sonic irradiation are pre- 

 sumably due to some modification of one or both of these special- 

 ized end-structures, possibly the splitting off of a peptide or other 

 small fragment. 



i 

 ■/it 



m\ > 



o,r^ 



B'B' 



A'B' 



A'A' 



Fig. 21. Whole polymeric SLS form from o solution sonically irradiated 

 480 min, showing the detailed band structure within an A'-B' junction, together 

 with the more commonly observed A'-A' and B'-B' junctions. Stained with PTA. 

 XI 20,000. (From Hodge, 1959b.) 



Occasional junctions of the type A'-B' have been observed in 

 polymeric SLS precipitates obtained from sonicated solutions of TC 

 (Fig. 21), and their band structure agrees well with that to be ex- 

 pected from an analysis of A'-A' and B'-B' junctions. The A'-B' 

 junctions have also proved useful in the detailed analysis of the 

 native-type (700 A-repeat) band pattern in terms of the SLS pattern. 



Effects of Proteases on Tropocollagen 



The effects of proteolytic enzymes such as trypsin, chymotrypsin, 

 and pepsin on the polymerization properties of tropocollagen macro- 

 molecules have been investigated in a recent series of experiments 

 (Hodge et ah, 1960). The results to date have been entirely con- 

 sistent with the end-chain hypothesis alreadv described. 



The data indicate that many solutions of "soluble collagen" are 

 relatively heterodisperse in that they contain variable amounts of 

 linear dimers, trimers, and higher polymers in addition to large 

 numbers of monomeric TC macromolecules. As indicated by the 

 viscosity data mentioned earlier, the proportion of polymers in- 

 creases as the pH is raised on the acid side of the isoelectric point. 

 The gross macroscopic appearance of the precipitates obtained on 



