The Determination of Amino Nitrogen. 177 



It has been found that every known amino acid obtained by 

 proteolysis, except prolin and oxyprolin, gives off one or more 

 atoms of nitrogen when treated with nitrous acid. 1 The dipeptids, 

 leucyl-leucin and leucyl-glycin, give off to nitrous acid only one 

 atom of nitrogen each, the atom in the peptid linking not being 

 removed. Glycin anhydride, containing two atoms of nitrogen, 

 both in peptid form, gives off no nitrogen at all. Peptides having 

 serin or glycin on the end of the chain containing the free amino 

 group may yield somewhat more than the theoretical one atom of 

 nitrogen, for reasons which will be shown later. With the excep- 

 tion of such peptides, which cannot be yielded by most proteins 

 in sufficient amount to interfere appreciably with determinations, 

 agreement between theory and results appears absolute. Native 

 proteins show but minimal amounts of amino nitrogen. The pro- 

 portion is greater in the primary albumoses, and still greater in 

 the deutero. (The albumose results will be published shortly with 

 Drs. Levene and Birchard.) The progressive increase of amino 

 nitrogen during hydrolysis is shown by the following series: egg 

 albumen in 2 per cent, solution was submitted to the action of 5 

 per cent, sodium hydrate at 6o°, 5 cubic centimeter samples being 

 drawn at intervals for amino determination. Addition of an oc- 

 casional drop of amyl alcohol during the earlier determinations is 

 necessary to prevent foaming of the viscous solutions. 



Time in hours. 



Per cent, of nitrogen 





in amino form. 



0 



3-0 



0-5 



7-15 



i-5 



10.31 



4-5 



19-45 



12.0 



28.22 



24.0 



39-02 



48.0 



46.62 



72.0 



54-02 



96.0 



61.10 



144-0 



68.42 



Completely hydrolized albumen contains 8.5 per cent, of its 

 nitrogen in amino form. 



A similar, but much more rapid increase was obtained when 



^Proc. of the Soc. for Exper. Biol, and Med., 1909, vii, 46. The apparatus in 

 improved form is manufactured by Machlett & Sons, New York. 



