INTERACTION OF COLLAGEN MAC ROMOLEC U L ES 33 



Under other conditions, and particularly in the presence of ATP, 

 the charge distribution on the protofibrils is such as to favor a 

 "polymeric segment" type of structure, i.e., one in which all like 

 features of the TC are in register across the fibril (Hodge and 

 Schmitt, 1960). In this type of structure (Figs. 6, 23), which we 

 have termed "fibrous-type segment long-spacing" (F-SLS) to dis- 

 tinguish it from the antiparallel FLS just described, the axial period 

 is equal to the length of the TC macromolecule, and the polarized 

 band pattern is equivalent to that obtained by placing single seg- 

 ments end-to-end in the sense AB-AB-AB-. If suitably oriented 

 fibers can be obtained from such preparations, it should be possible 

 to obtain direct evidence concerning the precise distribution of 

 density along the TC macromolecule by means of small-angle x-ray 

 diffraction. Such data cannot be obtained by x-ray analysis of 

 native-type collagen fibers, in which the TC macromolecules are 

 packed in a staggered fashion with respect to their neighbors. 



The ordered aggregation form of TC that is stable under physio- 

 logical conditions and that occurs in various connective tissues will 



Fig. 15. SIS aggregates of the fragment dimeric type CA'-A'C from a 

 solution sonically irradiated 240 min, showing extensive lateral aggregation in 

 the form of "ribbons." Stained with PTA. X 55,000. (From Hodge and Schmitt, 

 1958.) 



