PROTEINS 257 



(1) Perform the biuret, Millon and Adamkiewicz tests. The 

 biuret gives a redder color than with proteins. The Millon and 

 Adamkiewicz tests are usually faint or negative, since tyrosin 

 and tryptophane are split off early in the disintegration of pro- 

 tein. 



(2) Observe that peptones are not precipitated by concen- 

 trated nitric acid. 



(3) Try precipitation with picric acid, and with potassium 

 ferrocyanide in a solution made acid with acetic acid. 



(4) Recall that peptones are not coagulated by boiling. 



(5) The peptones diffuse through an animal membrane more 

 readily than do the proteoses. Since proteins do not diffuse, a 

 mixture of protein and peptones may be freed from peptones by 

 dialysis. 



(c) Peptids. Those decomposition products of the proteins 

 which are made up of a relatively small number of amino acids 

 are known as peptids, e.g. di-, tri-, tetra-, poly-peptids, etc., 

 according to the number of amino acids making up the peptid 

 molecule. The study of this group of protein derivatives 

 requires an amount of time obtainable only in a more specialized 

 course. 



(d) Amino Acids. The detailed study of these final products 

 of protein hydrolysis, as with the peptids, requires more time 

 than can be devoted to the subject in a general course in bio- 

 chemistry. Certain members of the group will be studied, how- 

 ever. 



i. The student should be furnished with a mixture of protein 

 decomposition products obtained by digesting protein material 

 for several days with trypsin. Test the liquid with the biuret 

 reaction. The result will give an idea of the stage to which the 

 digestion has progressed. Nearly neutralize 100 c.c. of the diges- 

 tion mixture with dilute hydrochloric acid. When nearly neutral, 

 exactly neutralize with 0.2% HC1 or with 0.2% sodium carbonate 

 to precipitate metaprotein. Filter, if necessary and concentrate 

 the nitrate, being careful to make the solution slightly acid with 

 acetic acid, as heating in alkaline solution will cause decomposi- 



