INTERACTION OF COLLAGEN MACROMOLEC U LES 



NATIVE TYPE 



43 



F-SLS 



Fig. 23. In the center is depicted a typical acid solution of collagen, con- 

 taining TC monomers together with some linear dimers, trimers, and other 

 n-mers. Under suitable conditions (e.g., dialysis against 1 per cent NaCI), the 

 solution yields native-type fibrils (top center), while the addition of ATP gives 

 rise to a polymeric SLS-type precipitate resulting from the growth of individual 

 segments on the pre-existing linear polymers of TC. At left is shown the linear 

 polymerization resulting from dialysis against distilled water, ultimately leading 

 to the formation of a water-clear gel consisting of very thin fibrils of native 

 type (top left). The addition of ATP during late stages of the dialysis leads to 

 the formation of polymeric SLS-type structures (F-SLS at bottom left). At right 

 is illustrated the depolymerizing action of proteases such as pepsin (see Fig. 22). 

 Subsequent dialysis against distilled water does not induce end-to-end poly- 

 merization (right center and top right), and the addition of ATP produces only 

 single segments, i.e., whole monomeric forms (bottom right). 



tions after treatment with either trypsin or pepsin (at appropriate 

 pH values ) produces a non-fibrous precipitate, eventually settling to 

 a dense mass at the bottom of the tube. When examined in the 

 electron microscope, such preparations exhibit only single segments, 

 with very few dimeric or higher polvmeric forms. It would seem, 

 therefore, that a hitherto unrecognized but important action of these 

 proteolytic enzymes on collagen in solution is a depolymerization 

 of protofibrils without apparent impairment of the three-stranded 

 helical structure of the individual macromolecules. This interpreta- 

 tion is supported by observations on the physical properties of col- 

 lagen solutions during attack by pepsin or trypsin. On exposure to 

 pepsin or trypsin (under suitable conditions of pH, temperature, 

 and ionic strength), the viscosity of collagen solutions undergoes a 

 small' but rapid decrease ( see also Gross, 1958 ) to a still high value 

 consistent with the presence of TC monomers in the solution (Fig. 

 22); the optical rotatory properties of the solution do not change 



