STRUCTURAL FACTORS INVOLVED IN 

 PROTEIN STABILITY 



W. Kauzmann, Frick Chemical Laboratory, 

 Princeton University , Princeton, New Jersey 



JTroteins are among the more temperature-sensitive components of liv- 

 ing systems, so that a discussion of the effects of temperature on proteins 

 is surely pertinent to the present symposium. The most important of these 

 temperature effects is the phenomenon largely responsible for the thermal 

 instability of proteins that is usually referred to as denaturation. The 

 present paper will be concerned with some aspects of this phenomenon. 

 Let us suppose that an investigator is fortunate enough to have isolated 

 some new protein from a living system and that he has decided to study 

 its stability. 



What are some of the factors that this investigator will have to keep 

 in mind in making such a study? He may be tempted to use the word 'de- 

 naturation' to describe his studies, and since the meaning of this word 

 has caused some misunderstanding, it is perhaps well to devote a few 

 paragraphs to it. The investigator will also have to decide on an experi- 

 mental approach to the problem of stability, and he will presumably 

 want to study the changes in some property that will tell him what is 

 taking place inside the protein molecule when it denatures. A brief survey 

 of some of the more useful methods available for studying changes in pro- 

 tein structure will therefore be given, special emphasis being placed on 

 two particularly important and convenient methods. General reviews of 

 the denaturation phenomenon have been given by Neurath et al. (24), 

 Haurowitz (9), Anson (1, 2), Putnam (26), Kauzmann (15) and Lumry 

 and Eyring (21). The significance of denaturation in various biological 

 processes has been discussed by Johnson, Eyring and Polissar (14). 



DEFINITIONS OF DENATURATION AND THE CONCEPT OF PROTEIN STABILITY 



When they are heated, many globular proteins lose the properties that 

 are responsible for the important role that they play in biological systems. 

 They may become insoluble in water at their isoelectric points and, if they 

 have any biological functions such as enzymatic activity, these functions 

 may be lost. The heated protein is said to be 'denatured'. Denaturation 

 in this sense (i.e. the loss of solubility in water or dilute salts at the iso- 

 electric point and the loss of any biologically significant activity that the 



