Nature of Amino Groups in Native Amino Proteins. 113 



without losing any of the accuracy of the original, is much more 

 convenient because it can be used an indefinite number of times 

 without disconnecting the parts, and the shaking by hand is 

 replaced by the less laborious and more efficient motor. The latter 

 also increases the rapidity, so that with one apparatus a deter- 

 mination can be made every seven or eight minutes. 



81 (690) 



The nature of the free amino groups in the native proteins. 

 By DONALD D. VAN SLYKE and F. J. BlRCHARD. 



[From the Rockefeller Institute for Medical Research, New York.] 



The fact that at least some proteins contain a small but definite 

 proportion of their nitrogen in the form of free amino groups ca- 

 pable of reacting with nitrous acid has been proven by one of us. 

 Levites and Skraup failed to obtain lysine from proteins which 

 had been treated with nitrous acid before hydrolysis. This 

 indicates that the w-NH 2 group of lysine, NH 2 • (CH 2 ) 4 • CH 2 (NH 2 ) - 

 COOH, may be free in the protein molecule. As lysine is peculiar 

 among the amino acids in possessing an w-NH 2 group, it appeared 

 possible that this might be responsible for all or most of the 

 amino nitrogen determined. We have, therefore, determined the 

 free amino nitrogen in ten proteins in which the lysine has already 

 been quantitatively determined in either our laboratory or in 

 Osborne's. 



Protein. 



Per Cent, of Total N in 



14 Lysine N. 



Free Amino N. 



Lysine. 





12.0 (Van Slyke) 



6.0 



S-6 



Fibrin 



1 1.4 (Van Slyke) 



5-7 



5-3 





8.5 (Van Slyke) 



4-25 



4-3 



Casein 



6.9 (Osborne) 



3-45 



3-4 



Gelatin 



6.3 (Van Slyke) 



3-15 



3-1 



Egg albumin 



4.0 (Osborne) 



2.0 



2.4 



Edestin 



3.8 (Van Slyke) 



1.9 



1.2 



Zein 



0.0 (Osborne) 



0.0 



0-3 



Albumoses from Witle Pepton. 





10.3 



5-15 



6-3 



Protoalbumose 



9.6 



4.8 



6.6 



Without exception the free amino N of the native proteins 



