REACTIOX.S OF PROTEIXS. "il 



3. Millon's Reaction. — (3n adding ilillon's reagent (a solu- 

 tion of mercurous and mercuric nitrates in nitric acid) to a protein 

 a red colour is produced. This is produced by all oxy-phenyl 

 compounds, and is given by the tyrosine group in proteins 



4. Adamkiewicz' Reaction. — On dissolving proteins in 

 glacial acetic acid, and adding strong sulphuric acid coloured 

 rings are formed at the junction of the two liquids. This reaction 

 is due to the presence of t^lyoxylic acid in the acetic acid, which 

 compound gives a blue or bluish-violet colour with tryptophane. 

 Hopkins and Cole, to make the test more certain, add glyoxylic 

 acid. 



5. Lieberman's Reaction. — Proteins which have been ex- 

 tracted with ether give a blue or bluish-violet colour on boiling 

 with strong hydrochloric acid. This reaction is really the same 

 as the above, as it is due to the presence of ;;]yoxylic acid or other 

 al(lc»hydic compounds in the ether. 



li. Ehrlich's Diazo Reaction. — On adding a diazonium salt 

 to a soluble protein, and making alkaline, a red colour is pro- 

 duced, if histidine or tyrosine be present in the molecule. .\ 

 diazotised solution of sulphanilic acid is convenient. Other 

 radicles give a yellow colour. 



7. Richmond and Miller's Diazo Reaction. — On diazo- 

 tising a solution of a protein, and adding an alkalim' solution of 

 /}-naphthol, a colour (usually yellow) is produced, and gas is 

 given off in the cold. This test proves the pre.-^ence of aryl and 

 acyl amino-groups respectively. 



8. The Halogen Reaction. — Chlorine and luomine L;ive 

 insoluble compounds with all soluble proteins. Iodine gives a 

 brown coloration. 



!•. Aldehyde Reactions. — On adding a solution of formalde- 

 hyde to a solution of a protein neutral to phenolphthalein it 

 becomes acid. This is characteristic of a-amino-acids, the basic 

 amino-group being converted into a very feebly basic methylene- 

 iunino-group. 



II). Ehrlich's Aromatic Aldehyde Reaction. — Certain 

 aromatic aldeln'des when added to proteins in acid solution 

 j;ive a well-marked coloured condensation product, ^-dimethyl- 

 amino-benzaldehyde and vanillin (p - hydroxy - m - methoxy - 

 benzaldehyde) give a red colour (the latter, however, tinged 

 with blue) and ju -nitro-benzaldehyde a green colour. This 

 ri'action appears to be characteristic of the tryptophane 

 radicle. 



11. On boiling most proteins with an alkali, a portion of the 

 sulphur is transformed into sulphide, which may be conveniently 

 demonstrated by the black colour i;iven on adding a snlution of 

 a lead salt. 



