176 



Scientific Proceedings (39). 



barium hydrate, from barium hydrate with carbon dioxide, and 

 at the end, an exact equivalent of sulphuric acid. This leaves only 

 the mono-amino acids in solution. It has been found that all 

 the known acids of this class react neutrally to indicators chang- 

 ing color at H + = io -7 , except the dicarboxylic acids, glutaminic 

 and aspartic, and these can be titrated accurately as monobasic 

 acids, even in the presence of the others, with rosalic acid as 

 indicator. The amino acids not precipitated by phosphotungstic 

 are, therefore, divided as follows: 



f Non-amino nitrogen, prolin, oxyprolin, tryptophane, and pos- 



Phosphotungstate I sibly unknown acids. 



filtrate i a • f Dicarboxylic acids (elulaminic and aspartic). 



Amino nitrogen < , ,. ,, . , . , . 



L I Mono-carboxyhc acids (teuctn, alanin, etc.). 



The method is being applied, among other things, to a study 

 of the fibrinoses in progress with Drs. Levene and Birchard in this 

 laboratory. 



1 12 (522) 



The determination of amino nitrogen as a measure of the rate 

 and extent of proteolysis. 



By DONALD D. VAN SLYKE. 



[From the Laboratories of the Rockefeller Institute for Medical 



Research.] 



Amino acids in proteins, as shown by Emil Fischer's work, are 

 undoubtedly bound together by peptid (-CO-NH-) linkings, the 

 nitrogen in these linkings being in the imino form. When hydroly- 

 sis occurs, the peptid linkings are split, yielding -COOH and -NH 2 

 derivations. The hydrolysis of each peptid linking, therefore, frees 

 an amino group. Consequently, determination of the amino nitro- 

 gen should afford direct chemical measure of the rate and extent 

 to which a protein is hydrolyzed, whether by action of acids, 

 alkalies or enzymes. It should also indicate the relative molecular 

 size of isolated intermediate products, such as albumoses, peptones 

 and peptids, as the larger molecules have relatively more nitrogen 

 in the peptide linkings, and less amino nitrogen. Results have 

 been obtained which indicate that the amino determination fulfills 

 the above requirements of the theory of protein structure, and that 

 it will be of practical value in the study of enzyme action and of 

 the products of partial hydrolysis. 



