On Plastein. 



II 



8 (346) 

 On plastein. 

 By D. D. VAN SLYKE and P. A. LEVENE. 



\_From the Rockefeller Institute for Medical Research^ 



" Plastein " is the name usually applied to the protein-like sub- 

 stance or substances precipitated from concentrated albumose 

 solutions by the action of enzymes. Of those who have investi- 

 gated the nature of plasteins, some have agreed that they are 

 resynthesized proteins, resulting from the reversibility of the hy- 

 drolytic reaction ; others view them merely as albumoses separating 

 from the concentrated solutions because of a lack of proper condi- 

 tions to maintain solubility ; while still others regard them as the 

 insoluble simple products of further digestion of the albumoses. 



Because, probably, of the small yields in which plasteins are 

 obtained, no investigator has hitherto performed a systematic esti- 

 mation of the hydrolytic products, although such estimations fur- 

 nish at present our most significant data concerning the nature of 

 proteins. We have hydrolyzed 1 30 g. of plastein obtained by the 

 action of pepsin upon Witte peptone. For comparison we tabulate 

 with our results those obtained by Brunner in Fischer's laboratory 

 from fibrin, the mother protein of the plastein. 



From 100 g. plastein From 100 g. fibrin (Brunner) 



Tyrosine 3.03 3.1 



Glycocoll 0.50 2.2 



Alanine ? 3. 1 



Valine "I 15 59 Present 



Leucine J 13.0 



Phenylalanine 1. 20 1.2 



Glutaminic acid 10.02 6.8 



Aspartic acid 2.15 I.7 



Proline 2.55 2.4 



Histidine 0.43 Not determined 



Arginine 2.06 " 



Lysine 1.42 " 



Tryptophane Present Present 



Total determined 38. 95 33-5 



Of the thirteen amino-acids tested for in plastein the presence 

 was proved of all except alanine, which was not isolated in pure 



