7] DIALYSIS STUDIES 111 



The effect of urea at 25° is shown in Table 4. Again there is good correla- 

 tion with the known effect of various concentrations of urea on these pro- 

 teins. The tendency to unfold could be followed by viscosity measurements 

 or by measuring specific optical rotations. Thus far, only the latter has been 

 studied. A solution giving an increase in optical activity has also shown 

 a decrease in escape rate, both in the urea studies and in the pH studies. 



Proteins are known to associate in a favorable environment to give dimers, 

 trimers, etc. Indeed, with certain representatives this tendency has been so 

 strong that the smallest dissociable unit has been recognized only after pro- 

 longed study. Insulin has been an example of this type of substance,^^ but 

 was finally recognized as having a dissociable unit as small as 6,000. This 

 value fits very well into the series in Table 1. The escape curve in 0-lN 

 acetic acid and 20/32 Visking for material purified by countercurrent dis- 

 tribution (CCD) is shown in Fig. 4. The escape curve for a sample of amor- 

 phous commercial insulin is also shown. Perhaps, in this latter a certain 



• Insulin A peak 

 o Amorphous insulin 



\t 16 

 Hours 



20 



24 



28 



Fig. 4. Escape rate curves with insulin preparations. 



percentage of the molecules have already begun to associate preliminary to 

 the formation of insoluble fibrils. ^^ Irrespective of the truth of this possi- 

 bility, when insulin is brought into solution at a concentration of 1 % with 

 a minimal amount of ammonia the pH is about 8-0, and when this solution 

 is placed inside the sac of the cell with water outside, the protein will not 



