150 PROTEINS AND AMINO- ACIDS [ch, 



Isoleucine has been extracted from seedlings of Vicia sativa. 

 Aspartic acid. The amide of this acid, i.e. asparagine, 

 CONHa'CHg-CHNHg-COOH 

 is widely distributed in plants. It is present in shoots of Asparagus 

 from which it derives its name. It has also been extracted in very con- 

 siderable quantities from etiolated seedlings of Vicia, Lupin, and from 

 various plants such as Potato, Dahlia, Garden Nasturtium (Tropaeolum),. 

 Cucurhita and Sunflower {Helianthus). 



Expt. 140. Preparation of asparagine from shoots of Asparagus (Asparagus 

 officinalis). Weigh out 500 gms. of shoots of asparagus and pound them in a mortar. 

 Put the mass in a large evaporating dish, add 500 c.c. of water and heat on a water- 

 bath. Squeeze the mass through linen and heat the fluid to boiling in a dish. Filter 

 off" the coagulated protein and to the filtrate add tannic acid (to precipitate the 

 remaining proteins, proteoses and peptones) until no more precipitate is formed. 

 Filter and remove any excess of tannic acid by adding a concentrated solution of lead 

 acetate drop by drop. Filter oflf the precipitate and remove any excess of lead acetate 

 with dilute sulphuric acid. Again filter and finally precipitate the asparagine by 

 adding a concentrated solution of mercuric nitrate (acidify the solution when making 

 with a few drops of nitric acid) until no further precipitate is formed. Filter off" the 

 mercury precipitate, suspend it in 150-200 c.c. of water, warm slightly and pass sul- 

 phuretted hydrogen through until the precipitate is decomposed. Filter oflF the 

 mercuric sulphide, and suck air through the solution until it ceases to smell of 

 sulphuretted hydrogen. Neutralize the solution and concentrate on a water-bath to 

 a small bulk. Then add about an equal volume of 98 'Yo alcohol. Crystals of asparagine 

 will separate out. Filter off" these on a small conical porcelain funnel, wash with 

 alcohol and dry. 



Make a solution of the asparagine (or use the commercial substance) in water and 

 perform the following tests : 



(a) Add a saturated solution of copper acetate. A blue crystalline precipitate of 

 the copper salt of asparagine separates out. Its appearance is hastened by shaking 

 or rubbing. 



(6) Boil 2-3 c.c. of the solution with one c.c. of 40% caustic soda solution. 

 Ammonia is evolved and may be detected by holding red litmus paper in the mouth 

 of the test-tube. Fumes of ammonium chloride will also be formed by introducing 

 a glass rod moistened with strong hydrochloric acid into the tube. 



Glutaminic acid. The amide, again, of this acid, i.e. glutamine, 



CONH2CH2'CH2-CHNH2COOH 



is widely distributed. It has been isolated from seedlings of Cucurhita^ 

 Lupinus, Helianthus, Castor-oil plant (Ricinus), Spruce Fir (Picea 

 excelsa) and a number of Cruciferae. 



Bxpt. 141. Preparation of glutaminic acid from gluten (from Cole, see p. 10). 

 Prepare gluten from 100 gms. of flour. This should give about 20 gms. of the dry 

 product. Divide the gluten into small pieces and dissolve it in 150 c.c. of concen- 



