128 THE PROTEINS AND PROTEASES [ch. 



Expt.125. lleactioiis of metaprotein. Dissolve about 1 gm. of edestiii (.see Expt. 133) 

 in 50 c.c. of a 2 "/„ hydrochloric acid and keep on a boiling water-bath for 2 hrs. 

 Neutralize with dilute sodium carbonate solution. A copious precipitate of meta- 

 protein separates out which is insoluble in water. Filter off the precipitate and 

 wash. Make with it the following tests : 



(a) Dissolve up some of the precipitate again in 0-4 "/(i hydrochloric acid. To 

 portions of the solution add : (i) Dilute sodium carbonate : the metaprotein is pre- 

 cipitated again and redissolves in excess, (ii) Concentrated hydrochloric acid : the 

 metaprotein is precipitated, (iii) Boil some of the acid solution. No coagulum is 

 formed : the metaprotein is not precipitated by boiling when in solution, and can 

 still be precipitated by neutralizing with sodium carbonate. 



(6) Suspend some of the precipitate in water and boil. Cool and add 0*4 % 

 hydrochloric acid : the precipitate is now insoluble, since the metaprotein is coagu- 

 lated when boiled in suspension. 



(c) To some of the precipitate suspended in water, add gradually saturated 

 ammonium sulphate solution : the metaprotein is insoluble in all concentrations of 

 the salt. 



Proteoses (albumoses) and peptones. These substances are formed 

 as products of hydrolysis by enzymes. When present in extracts from 

 seeds, however, it is sometimes uncertain whether they formed original 

 constituents of the seeds or resulted from hydrolysis. 



As a result of the enzyme hydrolysis of proteins a mixture of various 

 proteoses is usually produced (Chittenden and Mendel, 4) which can be 

 separated by various methods, such as different solubilities in ammonium 

 sulphate, alcohol, etc. The albumoses are soluble in water, salt solutions, 

 dilute acids and alkalies. They are all precipitated by complete satura- 

 tion with ammonium sulphate, and some by half-saturation with the 

 same salt. On the whole, they give the general colour reactions of the 

 proteins, and are precipitated by the protein precipitants, though some 

 groups of proteoses show certain exceptions. Their solutions are not 

 coagulated on boiling. 



The peptones are the only proteins not precipitated by complete 

 saturation with ammonium sulphate. They give the protein colour 

 reactions and are precipitated by tannic acid and lead acetate. 



Expt. 126. Separation and reactions of proteoses. Take 2 gms. of the globulin 

 edestin (prepared as in Expt. 133) and put in a flask with 100 c.c. of 0-2 % hydro- 

 chloric acid and warm until as much as possible of the edestni goes into solution. 

 Then cool and add O'o gm. of commercial pepsin : add also a little toluol, shake 

 and plug with cotton-wool. Leave in an incubator at 38° C. for 4 days. (A control 

 experiment should also be made with 100 c.c. of 0-2 % hydrochloric acid and 

 0-5 gm. of pepsin. Since pepsin itself gives a biuret reaction, a control is necessary 

 for comparison in the next experiment.) The preliminary changes in edestin hydro- 

 lysis are rapid, for it will be found that if the edestin solution is tested with sodium 



