REACTIONS OF PROTEINS 191 
OH aa OH OH 4H 
This compound possesses an amino group in place of a hydroxyl 
group and this amino group, to a certain extent, connects it with the 
proteins although it retains many of its carbohydrate properties. In 
light of the controversy concerning the action of bacteria on proteins 
their action on this compound is interesting. 
Meyer, in attempting to explain the action of bacteria on d-glucosa- 
min, studied the action on acetyl derivatives.’ He believes that the NH 
group is probably split off after which a further degradation takes place. 
Color Reactions of Proteins. By means of these much information 
may be secured concerning the amino-acids in a protein. 
Biuret Reaction. The protein solution is warmed and a little strong 
sodium hydroxide and dilute copper sulphate is added. Care should 
be exercised to use dilute copper sulphate two or three drops in a test 
tube of water. A violet color is obtained. The color is due to the 
formation of biuret, 
The test is given by those substances which have two CONH2 
sroups. 
Xantho-proteic Reaction. The protein is treated with concentrated 
nitric acid. The solution or protein will turn yellow. The presence 
of a CyoHs group is necessary. This reacts with the HNOs to yield 
nitro derivatives of benzine. Nitro-benzine is formed. 
Millon’s Reaction. The protein or protein solution is heated with 
Millon’s reagent. The protein is turned red or, if a solution is, used a 
reddish precipitate is formed. The reaction is given by those proteins 
which possess a hydroxy-phenyl group. Since tyrosine is the only 
amino acid having this group which has been isolated from proteins, 
the presence of this amino acid is indicated by a positive test with 
Millon’s reagent. Care must be exercised in the use of Millon’s reagent 
since it may be decomposed by some of the inorganic salts which precip- 
itate mercury. 
