PROTEINS 81 



amounts of nitrogen and C0 2 may be established. In case the 



CO. 



radicle R above contains no nitrogen -^ = 1 for the above com- 

 pound. If the radicle R contains nitrogen, however, as will be 

 the case if the compound contains diamino acids, or is a sub- 

 stance knoAvn as a peptid, in which two or more amino acids are 



CO 

 linked together, -^r^ will be less than 1. 



Oxidation. Oxidation of amino acids may yield a variety of 

 products according to the strength of the oxidizing agent. The 

 NH 2 groups are not split off by acids or by alkalies to any ex- 

 tent. Alkalies, however, split arginine into ornithine and 

 urea, and split off the sulphur from cystin and cystein. The 

 small amount of ammonia given off in acid hydrolysis of pro- 

 tein is believed to come from the few acid amid groups 

 CO NH 2 present. Oxidation with permanganate or hydro- 

 gen peroxide yields pyruvic acid from alanine. This compound 

 is interesting since it is believed to be one of the steps in the 

 breaking down of carbohydrates in the body, and thus may be 

 a substance by way of which amino acids and monosaccharides 

 can be converted into one another in the body. The substance 

 has the formula 



CH 3 



c = o 



COOH 



Nitrous Acid. With nitrous acid the oc amino acids are 

 broken down. Their nitrogen is liberated in the form of the 

 free gas. This will be recognized as the familiar reaction of 

 nitrous acid with primary amines. 



R NH 2 + HONO -> ROH + N 2 + H 2 



This reaction is the basis for the Van Slyke method for estimat- 

 ing amino acids, a method which has proven most useful in 

 helping to settle some of the difficult questions with .reference 

 to the fate of the proteins in the body. From this brief re- 



