PROTEINS 253 



vii. Glycoproteins and many phosphoproteins also are pre- 

 cipitated by acetic acid and dissolve in dilute alkalies. From 

 the above experiments, devise a way to distinguish among gly- 

 coproteins, phosphoproteins and nucleoproteins. 



5. Lecithoproteins. This group of conjugated proteins has 

 not been exhaustively studied. It includes compounds of simple 

 protein with the lecithins, the substances being known as leci- 

 thans, and also with some other members of the phosphatid 

 group. 



Derived Proteins 

 1. Primary Protein Derivatives. 



(a) Proteans. These protein derivatives are formed by the 

 action of very small quantities of acids, of water or of enzymes 

 on most of the proteins. They are characterized chiefly by al- 

 tered solubilities, as little is known of the proteans. 



(b) Metaproteins. By the further action of weak acids, or of 

 alkalies, products are formed which are readily soluble in weak 

 acids or alkalies, insoluble, however, in neutral solution. The 

 metaproteins are divided into two classes according to the manner 

 of their preparation. These substances often are called albu- 

 minates. 



i. Acid Metaprotein. 



Measure 25 c.c. of egg albumin solution (the solution furnished 

 will be egg white diluted 1 to 10) into a beaker, add an equal 

 volume of 0.4% hydrochloric acid and -heat on a water bath at 

 40-50 for about !/2 hour. While waiting, the preparation of 

 alkali metaprotein may be started, if time permits the study of 

 both of these substances. At the end of the heating period, boil 

 the solution vigorously. This will coagulate any unchanged 

 albumin. The metaprotein is not coagulated by boiling in acid 

 solution. Filter if necessary. 



Exactly neutralize the solution of acid albuminate with 0.4% 

 sodium hydrate. A white precipitate should form. This will 

 redissolve in a slight excess of alkali, so that the process of 

 neutralization must be carried on with great care. Filter off 



