INTERACTION OF COLLAGEN M AC ROMOLEC U LES 35 



])e referred to as the native tvpe. This form mav be reconstituted 

 from sohitions of TC under appropriate conditions (see Schmitt 

 cf al., 1955), has a fundamental axial period of about 700 A, i.e., 

 one-fourth the length of the TC macromolecule, and the intraperiod 

 liand distribution observed after electron staining is characteris- 

 tically asymmetric or "polarized" (Figs. 1, 7). As indicated diagram- 

 matically in these figures, the formation of native-type collagen 

 fibrils involves packing of protofibrils (linear polvmers of TC) so 

 that neighboring protofibrils are displaced longitudinally in relation 

 to one another by one-fourth of the TC length. That this must be 

 the case is readily apparent from the facts that ( a ) the axial period 

 of native-tvpe collagen is one-fourth that of the length of individual 

 macromolccules and (b) the additive sum of any asymmetric den- 

 sity distribution of length L displaced longitudinally and consecu- 

 tively by a distance L p, where p is an integer, results in the gen- 

 eration of an asymmetric density function of like "polarity" and 

 having an axial period of L/p. For native-tvpe collagen, p — 4. It 

 has been shown that other values of p pertain to other fibrous pro- 

 teins, e.g., paramyosin (Hodge, 1959a). In principle, it should be 

 possible to reconstruct the salient features of the band pattern of 

 native collagen bv a process of optical svnthesis from the band pat- 

 tern of SLS, and, in fact, such syntheses have been carried out in 

 this laboratory' (Fig. 8), with resolution limited only by the uncer- 

 tainties in the absolute positions of the various SLS bands intro- 

 duced by disordering during drying of the specimens for examina- 

 tion in the electron microscope. 



However, a more definitive proof of the correctness of the stagger 

 theory has been forthcoming in recent work (Hodge and Schmitt, 

 1960). In these experiments, fibrils of native type (700 A-repeat) 

 were placed in an environment containing monomeric TC under 

 conditions favoring the formation of SLS-type aggregates. It was 

 found that the TC macromolccules in the surfaces of the native-type 

 fibrils had apparently acted as "nuclei" for the growth of individual 

 segments (Fig. 9). In the resultant dimorphic ordered forms, which 



Fig. 16. Whole polymeric SLS form of sonicolly irradiated calfskin collagen, 

 showing isomorphous growth of fragment dimeric ribbons of the type CA'-A C. 

 Stained with PTA. X 74,000. (From Hodge and Schmitt, 1958.) 



Fig. 17. Whole polymeric SLS form of sonicolly irradiated calfskin col- 

 lagen, showing isomorphous growth of fragment dimeric ribbons of the type 

 CB'-B'C. Stained with PTA. X 100,000. (From Hodge, 1959b.) 



