The configuration of globular proteins in 

 aqueous solution and its dependence on pH 



CHARLES TANFORD 



Department of Chemistry 

 State University of Iowa, Iowa City, Iowa 



MACROMOLECULAR CONFIGURATIONS 



Any long chain molecule can acquire a very large number of possible spatial 

 configurations as a result of rotation about single bonds. Schematic dia- 

 grams representing some of the possible configurations of a linear polymer 

 without branching points or cross-links are shown in Fig. 1 . We are interested 

 in this paper in asking which of these or other configurations will actually 

 represent a given macromolecule in solution. The answer will clearly depend 

 on the affinity of the segments of the macromolecule for one another, the 

 affinity of solvent molecules for one another, and the affinity of chain seg- 

 ments for solvent molecules. It is profitable to define three extreme situa- 

 tions which may arise. 



(1) Random coiling. '^'^ Molecules are said to be randomly coiled if all pos- 

 sible configurations have the same energy. In that event, all spatial con- 

 figurations, such as those of Fig. 1 , occur with equal probabihty. Randomly 



(a) 



(e) 



Fig. 1 . Schematic representation of possible configurations of an unbranched polymer 

 chain. The fully extended length is the same for each configuration. 



