IX] PROTEINS AND AMINO- ACIDS 143 



(6) The remainder of the precipitate is boiled for a few minutes with dilute nitric 

 acid (1 part acid : 1 part water) in a test-tube. Then add an equal volume of 

 30 **/y solution of ammonium nitrate and 3-5 drops of concentrated nitric acid. Heat 

 to boiling and add 2 c.c. of a 3 ^/q solution of ammonium molybdate. A yellow pre- 

 cipitate of phosphomolybdate is produced. 



Derived Proteins. 



Metaproteins. These are hydrolytic products of albumins and glo- 

 bulins formed by the action of water or dilute acid or alkali. They are 

 insoluble in water, strong mineral acids and all solutions of neutral salts, 

 but are soluble in dilute acids and alkalies in the absence of any large 

 amount of neutral salt. 



Expt. 132. Reactions of metaprotein. Dissolve about 1 gm. of edestin (see Expt. 139) 

 in 50 c.c. of a 2^0 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% 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 0'4o/o 

 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 several 

 proteoses is usually produced 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 saturation 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. 



