HYDROLYSIS OF PROTEINS 89 



Ex. 50. Shake up 10 grams of flour in a flask with 50 c.c 

 of water and allow it to stand for six hours ; filter. 



Heat some of the filtrate and note the coagulation of a 

 vegetable albumin. In other portions of the watery extract 

 try the colour tests for proteins. 



5. Hydrolysis of Proteins. When proteins are 

 boiled with acids or alkalis, fused with caustic potash or 

 subjected to the action of superheated steam, they are de- 

 composed into simpler substances which do not give the 

 biuret reaction. By the hydrolysing action of boiling 

 hydrochloric or sulphuric acids the protein molecule is 

 split up into a great variety of degradation products, the 

 majority of which are amino-acids. Of these some 

 twenty or more different kinds have been isolated, the 

 chief of which, mentioned below, are found among the 

 dissociated products of practically all except the simplest 

 proteins. 



(1) The monamino acids most frequently obtained are : 

 alanine, phenylalanine, leucine, glutamic, and aspartic 

 acids. They are all crystalline bodies with a sweetish 

 taste. 



(2) Certain diamino acids are constantly found, 

 namely : arginine, lysine, and histidine. These are 

 strongly basic substances. 



(3) Tyrosine, a hydroxyamino acid, is present in 

 nearly all proteins except gelatine and some protamines, 

 and 



(4) Tryptophane also. The two last are easily 

 detected in a free or combined state by their colour 

 reactions (see pp. 85-86). 



(5) In most cases the sulphur in the molecule is split 

 off as cystine or cysteine. 



