The Tropocollagen Macromolecule and Its 

 Properties of Ordered Interaction ~ 



Alan J. Hodge '^ and Francis O. Schmitt "* 



The discovery that collagen in sokition exists in the form of dis- 

 crete monomeric macromolecular units, termed "tropocollagen" 

 (TC) by Gross et al. (1954), and consists, in all probability, of 

 several polypeptide chains arranged in a specific coiled configura- 

 tion, has had important consequences in the investigations of the 

 chemistry of connective tissue, in the biomedical field, and in fields 

 of special application such as the chemistry of leather. The detailed 

 examination of the various ordered aggregation states of the TC 

 macromolecule in the electron microscope and, in particular, the 

 examination of the so-called "segment long-spacing" form (SLS), 

 which is in effect a "molecular fingerprint" in that it indicates the 

 distribution of polar side-chains, have resulted in the formulation 

 of a mechanism for the end-to-end linkage of the macromolecules, 

 a process presumably involved in fibrogenesis in vivo. The precise 

 packing arrangements of TC in the various ordered aggregation 

 states are now known in detail, and it is on the basis of the specific 

 stereochemical configurations of the polar side-chains in these vari- 

 ous forms that a mechanism for calcification has been advanced by 

 Glimcher et al. ( 1957 ) . The experimental evidence indicated that 

 only the specific steric arrangement present in the "native-type" 

 aggregation state was capable of initiating nucleation of hydroxy- 



' The substance of this paper was also presented by one of us ( F.O.S. ) at the 

 Sixth Congress of the International Union of The Leather Chemists Society, Munich, 

 Germany, September 8, 1959 (Schmitt and Hodge, 1960). The German translation 

 was published in Das Leder. 



- This investigation was supported by a research grant, E-1469, from the National 

 Institute* of Allergy and Infectious Diseases, National Institutes of Health, U. S. Public 

 Health Service. 



^ California Institute of Technology, Pasadena, California. 



■* Massachusetts Institute of Technology', Cambridge, Massachusetts. 



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