LESSON XVII 



THE PEOTEQSES 



1. Witte's peptone contains very little true peptone, but consists chiefly 

 of proteoses, which are soluble like peptone, in neutral saline solutions. 



2. Make a solution of this substance in 10-per-cent. sodium chloride 

 solution, and filter. Very little residue is left on the filter. This consists of 

 dysalbumose, an insoluble form of hetero-albumose, formed during the pro- 

 cess of preparing the substance. If hot saline solution is used instead of cold 

 as a solvent, this amount of insoluble residue is increased, hetero-albumose 

 being to a slight extent precipitated by heat. 



3. The solution gives the following tests : 



(a) It does not coagulate on heating. 



(b) Biuret reaction (due both to peptone and proteoses). 



(c) A drop of nitric acid, best added by a glass rod, gives a precipitate 

 which dissolves upon heating and reappears on cooling. (This is due to the 

 proteoses present.) 



(d) The precipitate produced by the addition of acetic acid and a drop of 

 potassium ferrocyanide is also soluble on heating, and reappears on cooling. 



4. For the separation of the proteoses and peptone proceed as follows : 



(a) Saturate the solution with ammonium sulphate, and filter. The 

 filtrate contains the peptone, and the precipitate the proteoses. The peptone 

 is not precipitated by nitric acid, nor by most of the reagents that precipitate 

 other proteins. It is precipitated completely by alcohol, tannin, and potassio- 

 mercuric iodide ; imperfectly by phospho-tungstic andphospho-molybdic acid. 



It gives the biuret reaction, but in the presence of ammonium sulphate a 

 large excess of caustic potash is necessary. 



(b) Dialyse another portion of the solution; hetero-proteose is pre- 

 cipitated. 



(c) Saturate another portion of the solution with sodium chloride (or half 

 saturate with ammonium sulphate) after faintly acidulating with acetic acid. 

 Proto-proteose and hetero-proteose are precipitated. Filter. The filtrate 

 contains the deutero-proteose and peptone. 



The proto- and hetero-proteose may be redissolved by adding distilled 

 water, and may be separated from each other by dialysis (see b). 



Deutero-proteose may be separated from the peptone by saturation with 

 ammonium sulphate, or by the addition of a crystal of phosphoric acid. 

 These reagents precipitate the deutero-proteose, but not the peptone. 



Deutero-proteose gives the nitric acid reaction (see 3. c) characteristic of 

 the proteoses only in the presence of excess of salt. If the salt is removed 

 by dialysis, nitric acid then causes no precipitate. 



