200 EMIL L. SMITH, ROBERT L. HILL AND J. R. KIMMEL [1 



T 



>- 04 — 



Fig. 7. Chromatography of a partially autodigested preparation of papain in 0-2 m 

 phosphate buffer at pH 6-1 on a 1-3x30 cm. column of IRC-50. Activity (in arbitrary 

 units) of individual fractions towards benzoyl-L-argininamide is indicated. (Finkle and 

 Smith, unpublished.) 



may be assumed that autolytic cleavage at the A^-terminal region will pro- 

 duce active fragments of the papain molecule, whereas a primary cleavage 

 at or near the C-terminal region will result in the formation of inactive 

 fragments. Present evidence suggests that most of the fragments are en- 

 zymically inactive. 



The results obtained both by digestion with the aminopeptidase and by 

 autodigestion indicate that only a portion of the papain molecule is con- 

 cerned both in the catalytic activity of the enzyme and in determining speci- 

 ficity. The findings suggest that it will be unnecessary to determine the 

 complete structure of the protein in order to understand the properties and 

 mechanism of action of the enzyme. 



KINETIC STUDIES 



Evidence concerning the nature of the active region of an enzyme can fre- 

 quently be derived from a study of the kinetic behavior of an enzyme- 

 substrate system. For this reason, detailed kinetic studies with papain and 

 a variety of synthetic substrates are being performed. Only one phase of 

 these investigations will be discussed here since they have yielded some 

 information on the enzyme groupings which participate in the enzyme- 

 substrate interaction. 

 The usual formulation of the kinetics of an enzyme reaction is 



ki ko 



E+S ^=^ ES > P+E 



k-i 

 where E is enzyme, S substrate, P products and ES the enzyme-substrate 



