PROTEINS 115 



EXPERIMENTS ON PROTEANS 



Preparation and Study of Edestan. Prepare edestin according to the direc- 

 tions given on page 109. Bring the edestin into solution in 0.2 per cent hydro- 

 chloric acid and permit the acid solution to stand for about one-half hour. 1 Neutral- 

 ize with a 0.5 per cent, solution of sodium carbonate, filter off the precipitate of 

 edestan and make the following tests: 



1. Solubility. Try the solubility in water, sodium chloride, dilute acid and 

 alkali. Note the altered solubility of the edestan as compared with that of edestin 

 (see page 109). 



2. Millon's Reaction. 



3. Coagulation Test. Place a small amount of the protean in a test-tube, 

 add a little water and boil: Now add dilute hydrochloric acid and note that 

 the protein no longer dissolves. It has been coagulated. 



4. Tests on Edestan Solution. Dissolve the remainder of the edestan pre- 

 cipitate ino.2 per cent hydrochloric acid and make the following tests: 



(a) Biuret Test. 



(b) Influence of Protein Precipitant*. Try a few raetein precipitants such as 

 pier ic. acid and mercuric chloride. 



METAPROTEINS 



The metaproteins are formed from the native simple proteins 

 through an action similar to that by which proteans are formed. In 

 the case of the metaproteins, however, the changes in the original pro- 

 tein molecule are more profound. These derived proteins are char- 

 acterized by being soluble in very weak acids and alkalis, but insoluble 

 in neutral fluids. The metaproteins were formerly termed albuminates , 

 but inasmuch as the termination ate signifies a salt it has always been 

 somewhat of a misnomer. 



Two of the principal metaproteins are the acid metaprotein or so- 

 called acid albuminate and the alkali metaprotein or so-called alkali 

 albuminate. They differ from the native simple proteins principally in 

 being insoluble in sodium chloride solution and in not being coagulated 

 except when suspended in neutral fluids. Both forms of metaprotein 

 are precipitated upon the approximate neutralization of their solutions. 

 They are precipitated by saturating their solutions with ammonium sul- 

 phate, and by sodium chloride also, provided they are dissolved in 

 an acid solution. Acid metaprotein contains a higher percentage of 

 nitrogen and sulphur than the alkali metaprotein from the same source, 

 since some of the nitrogen and sulphur of the original protein is liberated 

 in the formation of the latter. Because of this fact, it is impossible 

 to transform an alkali metaprotein into an acid metaprotein, while it 

 is possible to reverse the process and transform the acid metaprotein 

 into the alkali modification. 



1 The edestan solution preserved from experiment (5), p. no, may be used. 



