178 CHEMISTRY OF PLANT LIFE 



tryptophane. It is not sufficient to support animal life and 

 promote growth, if used as an exclusive source for protein for food. 



THE EXTRACTION OF PROTEINS FROM PLANT TISSUES 



Since proteins are indiffusible, it is essential that the cell- 

 walls of the tissue shall be thoroughly ruptured as the first step in 

 any process for the extraction of these compounds from plant tis- 

 sues. This is usually accomplished by grinding the material as 

 finely as possible, preferably with the addition of sharp quartz 

 sand, or broken glass, to aid in the tearing of the cell-wall material. 



The solvent to be used in extracting the proteins from this 

 finely ground material depends upon the nature and solubility 

 of the proteins which are present, and also upon whether it is 

 desired to separate the proteins which may be present in the plant, 

 during the process of the extraction. A glance at the scheme of 

 classification of the proteins will show the following solubilities 

 which serve as a guide to the procedure to be followed: (a) pro- 

 teoses, albumins, and some globulins may be extracted with water; 

 (6) globulins and most of the water-soluble proteins may be 

 extracted by using a 10 per cent solution of common salt; (c) 

 prolamines are extracted by 70-90 per cent alcohol; glutelins and 

 prolamins dissolve in dilute acids or dilute alkali. 



A common procedure is to extract groups (a) and (6), using a 

 10 per cent salt solution as the solvent, and then to separate the 

 albumins, globulins, etc., from this solution by suitable precip- 

 itants; then to treat the material with 80 per cent alcohol, to 

 extract the prolamines; and finally with dilute alkali, to extract 

 the glutelins. The dissolved proteins in each extract can be sub- 

 sequently purified by dialysis, precipitation, etc. The insoluble 

 proteins can be studied only after removing the other materials 

 associated with them in the tissue, by suitable mechanical or chem- 

 ical means. 



THE SYNTHESIS OF PROTEINS IN PLANTS 



The synthesis of proteins in plants is not a process of photo- 

 synthesis, as it can take place in the dark and in the absence of 

 chlorophyll, or any other energy-absorbing pigment. However, 

 protein-formation normally takes place in conjunction with car- 



