vm] THE PROTEINS AND PROTEASES 129 



chloride solution even after 24 hours in the incubator, no precipitate will be given 

 with sodium chloride, in contrast with the copious precipitate given on the addition 

 of salt solution to the unaltered acid solution of edestin (see also Expt. 124). After 

 four days, the incubated mixture is neutralized with dilute sodium carbonate 

 solution, filtered and saturated while boiling with solid ammonium sulphate. 

 A precipitate of proteoses is formed, which can be gradually collected together as 

 a sticky mass and removed with a glass rod. Dissolve the precipitate in some hot 

 water, filter and make the following tests : 



(a) Xanthoproteic reaction. Add a few drops of nitric acid. It is characteristic 

 of most proteoses that a precipitate is formed which disappears on heating and 

 reappears on cooling. In the case of the proteoses from edestin, only a slight pre- 

 cipitate may be given, but it is increased by adding a little sodium chloride solution. 

 The colour is intensified in the usual way by addition of ammonia. 



(b) Millon's reaction. A positive result is given. 



(c) Glyoxylic reaction. A positive result is given. 



(d) Biuret reaction. A pink or pinkish-violet colour is given. 



(e) Sulphur reaction. A positive result is given. 



(/) Add a little tannic acid solution. A precipitate is formed. 



(<7) Add a drop of copper sulphate solution. A precipitate is formed. 



(Ji) Add a drop of strong acetic acid and then a couple of drops of potassium 

 ferrocyanide. A precipitate is formed which disappears on heating and reappears 

 on cooling. 



(i) Boil some of the solution. No coagulum is formed. 



Expt. 127. Detection of peptone. The saturated solution, from which the proteoses 

 have been precipitated, is then filtered and to a measured quantity (about 5 c.c.) 

 twice the volume of 40 % sodium hydroxide is added and a drop of 1 / copper 

 sulphate solution. A pink colour appeal's, due to the presence of peptone. A test 

 should be made with the control solution containing hydrochloric acid and pepsin 

 only. An adequate amount should be saturated with ammonium sulphate, filtered 

 and 5 c.c. tested for peptone. The reaction is less marked than in the actual hydro- 

 lytic product. Concentrate the remainder of the peptone solution on a water- bath 

 and pour off from the excess of ammonium sulphate crystals. Filter and make 

 the following tests : (i) Xanthoproteic, (ii) Millon's, (iii) Glyoxylic, (iv) Tannic acid. 

 A positive result is obtained in each case. 



THE SEED PROTEINS OF CERTAIN PLANTS. 



The proteins present in the seeds of certain genera and species, upon 

 which special investigations have been made, may now be considered. 



It should be borne in mind that there are always several proteins 

 present in the seed. Some are reserve proteins of the cells of the 

 endosperm or of the storage tissue of the cotyledons : others are proteins 

 of the protoplasm and nuclei of the tissues of the embryo and of the 

 endosperm. 



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