W. KAUZMANN 23 



equivalent to any ellipsoid. The changes in optical rotation that occur on 

 denaturation are often attributed vaguely to changes in the contributions 

 of asymmetric carbon atoms present in the protein molecule. This termi- 

 nology is inappropriate because the magnitude of the optical rotation 

 depends only very indirectly on the presence of asymmetrical carbon atoms 

 in a molecule. The important factor is the vicinal actions of groups on each 

 other. These interactions change whenever the relative spatial positions 

 of groups are changed. Therefore the optical rotation of a protein will 

 change whenever the polypeptide chain is twisted into a new conformation 

 even though no change may have taken place in the asymmetric carbon 

 atoms themselves. Some interesting recent studies of the viscosity and 

 optical rotation changes on denaturation are discussed. 



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