l62 



PHYSIOLOGY OF NUTRITION 



The finely powdered seeds are treated with a io-per cent, solution of sodium 

 or ammonium chloride and the solution is filtered off after twenty-four hours. 

 The filtrate is then dialysed, Kuhne's dialyser being well suited to this purpose 

 (Fig. 86). The solution is placed in a tube of parchment paper surrounded by 

 running water. The water enters through the funnel, in the diagram, and 

 escapes through the lateral tube. After two or three days the globulin is found 

 to have settled upon the bottom of the parchment paper tube, as a tough, viscous 

 mass, insoluble in pure water but soluble in solutions of neutral salts. The 

 globulins obtained from different plants are not identical. So are distinguished, 

 for example, edestin (from fatty seeds, such as those of hemp, Cannabis sativa), 

 legumin (from pea and other legume seeds), and conglutin (from lupine seeds). 

 The phytoglobulins are not altogether the same as the typical animal globulins. 

 Peptones are present in plants only in very small amounts. To isolate these 

 Neumeister 1 has made use of their solubility in saturated ammonium sulphate 

 solution. All other proteins are precipitated by this salt. Aqueous extracts 

 of seeds and plants are saturated with solid ammonium sul- 

 phate and then filtered. The filtrate gives the color reaction 

 of the biuret test for peptones. The plants studied by 

 Neumeister may be assorted into two groups according to 

 their peptone content. Seeds of Papaver (poppy), Beta 

 (beet), Hordeum (barley), Zea (maize), and Triticum (wheat), 

 contain no trace of peptones; these substances being here de- 

 tected only during germination. In seeds of Lupinus (lupine), 

 Vicia (vetch), and Avena (oats), however, which belong to the 

 second group, peptones are more plentiful than in the seedlings. 

 The peptones thus act here as reserve food and are gradually 

 used up during germination. 



An idea of the structure of the proteins may be derived 

 from the study of their cleavage products. The products of 

 complete hydrolysis, 2 obtained by continued boiling with concentrated acids 

 and alkalis, or through enzymatic decomposition, are mainly amino acids. The 

 following principal products of the hydrolysis of simple proteins have already 

 been isolated and identified. 6 



i. Aliphatic Compounds 

 A. Monoamino acids 



Glycocoll (a-amino-acetic acid), CH 2 NH 2 COOH. 



d-Alanin (a-amino-propionic acid), CH 3 CHNH 2 COOH. 



/-Serin (a:-amino-/3-hydroxypropionic acid, a-amino-/3-lactic acid), 



CH 2 OHCHNH 2 COOH. 



1 Neumeister, R., Ueber das Vorkommen und die Bedeutung eines eiweisslosenden Enzyms in jugend- 

 lichen Pflanzen. Zeitsch. Biol. 30 : 447-463. 1894. 



2 Abderhalden, E., Neuere Ergebnisse auf dem Gebiete der speziellen Eiweisschemie. Jena, 1909. 



e The classification has been made clearer than in the German text, and the formulas are 

 here introduced. Formulas are more clearly given in: Mathews, Albert P., Physiological 

 Chemistry. 3d ed. n 54 p. New York, 1920. — Ed. 



\2t7 



Fig. 86. — Kuhne's 

 dialyser. 



