Smithsonian Report. 1951. — Kilby 



PLATE 1 



1. l^holonucrogiaph of pepsin crssials, X 80. 

 (From Enzymes, by Sumner and Somers.) 



2. Photomicrograph of trypsin crystals, X 

 250. (From Crystalline Enzymes, by 

 Northrop, Kunitz, and fierriott.) 











^> 



c 



^ 



^ 







^ 



3. Photomicrograph of trypsinogen, X 250. 

 This is the inactive precursor of the digest- 

 ive enzyme trypsin. (From Crystalline 

 Enzymes, by Northrop, Kunitz, and Hcr- 

 riott.) 



S^ O ^ ^ 

 C ^^ r 



4. Pliotomicrograph of urease crvstals, X 800. 

 This enzyme was the first one to be ob- 

 tained as crystals. (From Enzymes, by 

 Sumner and Somers.) 



