I W. KAUZMANN 13 



in the property): 1) Solution viscosity. 2) Friction ratio (as determined 

 from the molecular weight and the diffusion constant). S) Rotatory dif- 

 fusion constants (as determined from flow birefringence, the decay of the 

 Kerr effect, and the dei^olarization of the fluorescence from adsorbed or 

 coupled dye molecules). 4) Dissymmetry of light scattering. 5) Low angle 

 x-ray scattering. 6) The second virial coefficient of the osmotic pressure 

 (or light scattering) under conditions that suppress electrostatic interac- 

 tions between molecules (i.e. moderate salt concentrations). 



Short-range Properties: 1} The infra-red absorption spectrum. 2} The 

 visible and ultra-violet absorption spectrum. 3) The partial specific vol- 

 ume. (Small changes during denaturation are readily measured in dila- 

 tometers.) 4) The refractive index increment (small changes during de- 

 naturation are readily measured by means of an interferometer.^) 5) 

 Optical rotation. 6} Dissociation constants of acidic and basic groups. 

 (Changes in dissociation constants result in the release or absorption of 

 hydrogen ions which can be followed readily as a function of time by 

 means of recording pH-stats, such as those of Jacobsen and Leonis (10) 

 and of Neilands and Cannon (23).) 7) Changes in the reactivities of other 

 groups, such as the sulfhydryl group. (The ease of exchange of deuterium 

 atoms with hydrogen atoms, w^hich has been studied recently by Linder- 

 strom-Lang and co-workers (20), is another example of a change in re- 

 activity resulting from denaturation.) 



Detailed reviews of the experimental measurement of shape properties, 

 as well as of their interpretation, have been given by Edsall (5), Gut- 

 freund (8) and Sadron (28). 



Since the structural information provided by the two classes of proper- 

 ties differs in its basic character, both classes are useful in detecting and 

 understanding the phenomenon of denaturation. Wherever possible, studies 

 of denaturation ought to include an investigation of the changes in at 

 least one property from each of the two classes. 



Unfortunately many of the properties that have been listed above are 

 not particularly well suited for more routine investigations of denatura- 

 tion, such as one would be likely to conduct in a preliminary study of the 

 stability of a newly isolated protein. For instance, the measurement of 



'In the case of the urea denaturation of ovalbumin it has been found (17) that 

 changes in the refractive index can be accounted for entirely in terms of the change 

 in volume that accompanies denaturation, assuming that the specific refractivity of 

 the solution, r = (n" — l)/(n- + 2)d, is a constant, where n is the refractive index 

 and d is the density of the solution. The fact that r is constant during denaturation 

 indicates that the polarizability of the protein molecule does not change dm-ing 

 denaturation, at least in the case of the urea denaturation of ovalbumin. Thus it 

 appears that the interferometer measures the same thing as the dilatometer does. 



