7] DIALYSIS STUDIES 109 



here to discuss the individual behavior of each solute, but a few generaliza- 

 tions seem to be appropriate. Firstly, the increase in molecular weight (M.W.) 

 consistently follows the same sequence as the decrease in escape rate, but 

 not in direct proportion. A relative increase in M.W. has a greater effect 

 as the maximum range of size capable of passing is approached. Thus the 

 rate ratio for bacitracin/subtilin in 20/32 casing is a little more than three- 

 fold, but in 18/32 casing it is more than six-fold. The selectivity, therefore, 

 becomes greater as the limiting size is approached. Since the list of proteins 

 in Table 1 includes acidic, neutral, and strongly basic ones with no obvious 

 effect on the relationship of escape rate to M.W., it would appear that 

 charge effects are relatively unimportant in the determination of escape rate. 



The results with two pairs of proteins are particularly striking. These are 

 trypsin-trypsinogen and chymotrypsin-chymotrypsinogen. Although each 

 enzyme is so closely related in size to its zymogen that the accepted methods 

 of molecular weight do not differentiate them, a striking difference in escape 

 rate is noted here. It would seem that this must reflect a difference in shape. 

 Indeed, such a theory is in line with the published results of Neurath and 

 co-workers.^ '^ 



If the escape rate of proteins in this type of cell is really governed almost 

 entirely by its overall outside dimensions, then the shape of the molecule 

 should also have a strong influence. The proteins in Table 1 are all known 

 to be quite globular in shape except under conditions which denature them. 

 We have accordingly investigated the effect of denaturing conditions on 

 dialysis rate. These include the effect of temperature, pH, urea, trichloro- 

 acetic acid, oxidation with performic acid, etc. In all cases where these 

 conditions are known to cause denaturation, reversible or otherwise, a 

 strikingly slower dialysis rate has been observed. 



Table 2 

 EFFECT OF TEMPERATURE (IN DISTILLED WATER) 



The effect of temperature is shown in Table 2. Ribonuclease is known^° 

 to undergo reversible unfolding at a temperature of 65°. This is reflected 

 here by a slower escape rate at 65° than at 41°. Lysozyme, on the other hand, 

 is known to be very stable and shows a faster escape rate at 65° than at 41° 

 One might infer from these data that a mixture of the two proteins could 



