6o 



GERTRUDE E. PERLMANN 



TABLE I 



Amino Acid Composition of Crystalline Pepsin [4] 



Nature of amino acid 



No. of residues 

 per molecule 



Per cent of 

 total 



That pepsin is a tightly folded molecule is indicated by its low intrinsic 

 viscosity. The question arose, therefore, as to whether or not reagents 

 could be found that would unfold the polypeptide chain and if unfolding 



100 



80 



60- 



^ 40 



20 



• Dilute HC 

 o •■ ■• + 8m urea 

 A ■• ■• + 3m 

 guanidine 

 hydrochloride 



1-0 20 30 40 5-0 



pH 



Fig. I. pH dependence of the activity of pepsin for the hydrolysis of haemo- 

 globin. 



occurred, how certain properties, such as viscosity, optical rotation and 

 the biological activity of the enzyme, would be affected. 



The first two reagents which were investigated for their effect on pepsin 

 were urea and guanidine hydrochloride which are known to have a pro- 

 found influence on the biological activity of enzymes, e.g. ribonuclease [5], 

 chymotrypsin [6] and trypsin [7]. In contrast to the enzymes, which are 



