PROTEINS 99 



enzymes, and to a certain extent by acids produces optically 

 active acids, either dextro- or levorotatory, but does not cause 

 racemization. 



Acids, Bases. The amino acids add on acids such as hydro- 

 chloric at the amino group. Thus 



H 

 -NH 2 + HCl- N = H 2 



Cl 



The acid raises the valence of the nitrogent to five. They also 

 interact with bases to form salts. 



- COOH + NaOH - COONa + H 2 



At the amino group the amino acids add on the salts of certain 

 metals such as cupric chloride, mercuric chloride, etc. This 

 property is often made use of to precipitate amino acids. 



Formaldehyde. With formaldehyde, amino acids form meth- 

 ylene compounds. The basic properties of the amino group are 

 thus greatly reduced, and the terminal carboxyl group can be 

 titrated with a standard alkali. On this process a much used 

 method for estimating amino acids is based (Sorensen's method). 



I ! 



HC NH 2 + H 2 CO - HC N = CH 2 + H 2 



COOH COOH 



Carbamino Reaction. The amino acids interact with carbon 

 dioxide in the presence of calcium salts to form carbamino com- 

 pounds. These have the following structure: 



K CH NH C = 



I I 



= C Ca 



If the nitrogen in this compound is determined, and also the 

 amount of CO., which is combined, a relationship between the 



