EXTRACTION 421 



40°. Chibnall * has devised a method for distinguishing 

 between the proteins of the cell sap of the central vacuole and 

 those contained in the cytoplasm of the cell. The method 

 consists in treating the fresh leaves with water containing 

 ether, to effect cytolysis, and pressing in a hydraulic press ; 

 the cake is then allowed to imbibe water and is once more 

 pressed without rupturing the cells. The liquid so obtained 

 presumably contains the proteins of the cell sap ; these are 

 precipitated with 30 per cent alcohol. In the case of the 

 spinach, this product contained 2-4 per cent nitrogen and con- 

 sisted of either globulin or albumin. The residual cake of 

 leaf tissue is ground with water, in order to break up the cells, 

 and the resulting colloidal solution is treated with acetic acid 

 which throws out a floccular precipitate. This precipitate 

 after purification, gave a white powder which contained 14-9 

 per cent of nitrogen ; it represents the cytoplasmic protein 

 and appears to be a type of protein hitherto unrecognized, 

 differing from other native proteins in being soluble in small 

 excess of either acid or alkali. 



Osborne, Wakeman, and Leavenworth f are of the opinion 

 that the protein in alfalfa leaf may be combined with a colour 

 complex of a fiavone nature and thus belongs to the class of 

 conjugated proteins ; their evidence for combination is the 

 fact that the protein is extracted only after prolonged heating 

 with alkali, during which period hydrolysis takes place 



EXTRACTION OF PROTEINS. 

 The main facts relating to the solubilities of the common 

 vegetable proteins are as follows : — 



1. Proteoses, albumins, and some globulins are soluble in 



water. 



2. Globulins, together with most of the proteins soluble in 

 water, dissolve in 10 per cent sodium chloride. 



3. Prolamins are soluble in alcohol (70-90 per cent). 



4. Glutelins and prolamins dissolve in dilute acid and in 

 dilute alkali. 



* Chibnall : " J. Biol. Chem.," 1923, 55> 333- 



t Osborne, Wakeman, and Leavenworth : " J. Biol. Chem.," 1921, 49, 



63- 



