CELL-CONTENTS AND CELL-WALLS. 



Of albumins, leucosin occurs in Wheat, etc., legu- 

 meliu in Broad Bean and Pea, ricin in Castor Oil. 



The chief glutelin known is the glutenin of Wheat. 



The chief prolamiiis are gliadin in Wheat, hordein 

 in Barley, zein in Maize. 



39. Conjugated Proteins. The nucleo-proteins, belonging 

 to this class, are important constituents of the cells of both animals 

 and plants, occurring especially in the nucleus. They contain phos- 

 phorus, and consist of protein combined with nucleic acid. They 

 probably do not occur as reserve proteins in seeds ; in the Wheat 

 grain, for instance, they are found in the embryo but not in the 

 endosperm. 



40. Derivatives of Proteins. Proteins when acted upon by 

 acids and alkalis, and by enzymes, are converted into (1) the meta- 

 proteins acid albumin and alkali-albumin ; (2) proteoses, 



formed from proteins by further action of acids and alkalis, and by 

 enzymes ; (3) peptones, formed from proteins by prolonged action 

 of acids, alkalis, and enzymes ; (4) amino acids, the ultimate pro- 

 ducts in tryptic digestion of proteins. Several polypeptides (most 

 of which are, as already stated, synthetic substances) have been 

 obtained from proteins by hydrolysis. 



The metaproteins, proteoses, arid peptones still show the properties 

 of proteins, but the amino acids do not. See 43, 56, 60. 



41. Experiments with Egg Albumin. Fora study 

 of the general reactions of proteins use white of egg, which 

 contains about 10 per cent, of protein, the greater part 

 being soluble albumin. 



Break three or four fresh eggs into a basin, keeping back 

 the yolks ; then beat up the white with an egg-beater, or 

 snip it in all directions with scissors so as to cut the mem- 

 branes in it and make it more readily soluble. Add about 

 100 c.c. of water for each egg used, transfer to a flask, and 

 shake vigorously ; the solution formed is somewhat opal- 

 escent, but becomes clear on addition of some common salt. 

 Test a portion of the solution with red litmus paper : the 

 reaction is faintly alkaline. Divide the solution into the 

 required number of portions, in test-tubes, for the follow- 

 ing colour and precipitate reactions (a to ?), most of which 

 apply to proteins in general. For s and t have ready a 

 hard-boiled egg. 



