36 



MACROMOLECULAR COMPLEXES 



allow a direct comparison of the band patterns of both the segment 

 and native forms, it is observed that each band in the native-type 

 fibril exhibits a direct transverse continuity with one of four differ- 

 ent bands of the segment pattern (Figs. 10, 11), each of different 

 intensity and separated longitudinally from one another by L/4, 

 where L is the length of the TC macromolecule. It is clear, there- 

 fore, that the density observed in any particular band of the native- 

 t\pe structure represents a summation of the densities of the ap- 

 propriate four "equivalent bands" in the segment-type structure. 

 It should be noted that, although the bands observed in SLS, 

 whether stained for basic or acidic side-chains, obey this selection 

 rule (i.e., may be classified in groups of four "equivalent bands" 

 spaced L/4 apart), this does not imply that the TC macromolecule 

 consists of four identical subunits. In any case, the physical prop- 

 erties of collagen solutions and the distribution of density in the 



Fig. 18. Composite micrograph for comparison of the band patterns of 

 whole monomeric forms (single segments, a and c) with that of the whole poly- 

 meric form (b). The use of two single segments is necessary since the band 

 pattern is often obscured at one or both ends by disorder resulting from drying 

 of the specimen. Arrow 1 indicates the new band observed in the B'-B' junc- 

 tions of polymeric SLS forms, which is not present in single segments, and 

 apparently is the result of end-to-end polymerization of the TC macromolecules. 

 Calfskin collagen. Stained with PTA. X 120,000. (From Hodge and Schmitt, 

 1958.) 



