166 THE PROTEIN SUBSTANCES. 



or spherical aggregations. It has a faint bitter taste, gives a crystalline hydro- 

 chloride which is slightly soluble in strong hydrochloric acid, and gives a crys- 

 talline copper salt. 



After describing the different amino-acids it remains for us to call 

 attention to certain general reactions of the amino-acids. 



By the action of formaldehyde the amino groups are changed into 

 methylene groups according to the scheme: 



R.CH.NH 2 R.CH.N : CH 2 



+H<30H= | +H 2 0. 



COOH COOH 



The amino-acids behave like neutral bodies while the methylene 

 combinations are acids and on this behavior is based SORENSEN'S l 

 formoltitration which serves for the estimation of amino-acids in the 

 urine (Chapter XIV) as well as to follow the progress of proteolysis. 

 As the proteolysis progresses and imide bindings are loosened a large 

 number of atomic complexes with free NH 2 and COOH groups are set 

 free. If now the NH 2 groups are fixed as methylene groups by the addi- 

 tion of formol, the complex behaves like acids and the number of their 



N 



COOH groups can be determined by titration with barium or sodium 



5 



hydroxide solution, using phenolphthalein or thymolphthalein as in- 

 dicator. With the presumption that for every COOH group set free 

 there existed a free NH 2 group the extent of the proteolysis can also 

 be expressed in milligrams N by multiplying the number of cubic centi- 



N 



meters alkali used by 2.8. 

 o 



SIEGFRIED has found that amino-acids in the presence of alkali or 

 alkaline earths de-ionize carbon dioxide and form salts of the type of 

 the carbamino salts, SIEGFRIED'S " carbamino-reaction." For example 

 glycocoll in the presence of lime yields with carbon dioxide, calcium 

 carbamino-acetic acid, CH 2 .NH.COO 



I I 



COO Ca 



If the nitrogen is determined and at the same time the combined carbon 

 dioxide estimated by means of the calcium carbonate split off on boil- 



r^o 

 ing the filtered solution, then the quotient - gives the number of N 



atoms for every molecule C0 2 taken up. This quotient is equal to 1 

 for glycocoll and the aliphatic amino-acids because these go over quan- 



1 Sorensen, Bioch. Zeitschr., 7; with Jessen Hansen, ibid., 7; with V. Henriques, 

 Zeitschr. f. physiol. Chem., 63 and 64; Henriques and Gjaldbak, Ibid., 67 and 75. 



