54 THE VEGETABLE PROTEINS 



sence of the above-mentioned dipeptide of proline and phenylalanine, 

 which required several hours' heating in a closed tube with concentrated 

 hydrochloric acid before it was completely hydrolysed. Gliadin when 

 boiled with 25 per cent, sulphuric acid for twelve hours yields a con- 

 siderable quantity of an insoluble product which resembles the sub- 

 stance usually regarded as humus. The writer, however, found that 

 this substance could be further decomposed by boiling with strong hydro- 

 chloric acid and that it then yielded several amino-acids, among which 

 glutaminic acid and cystine were conspicuous. Whether further study 

 of the time of hydrolysis required to completely decompose the animal 

 proteins will show them to be equally resistant to hydrolysis is a 

 question which cannot at present be answered. 



The amino-acids which have been obtained from vegetable proteins 

 are the same as those yielded by animal proteins, with the exception 

 of diamino-tri-oxy-dodecanic acid, which has thus far been found only 

 in casein (see Plimmer, The Chemical Constitution of the Proteins}. 

 Ammonia is also a constant product of their hydrolytic decomposition. 

 It is thus plain that no fundamental chemical difference exists in the 

 character of the amino-acids from which the molecules of the vegetable 

 proteins are constructed and those which form the molecules of the 

 animal proteins. The ideas which at one time appear to have been 

 held by some, that the vegetable proteins are fundamentally different in 

 their constitution from the animal proteins, has no foundation in fact, 

 for such differences as have been found consist chiefly in the proportion 

 in which some of the amino-acids are yielded by the vegetable proteins 

 as compared with the animal. In general the plant proteins yield 

 more glutaminic acid than the animal and many of them also yield 

 more ammonia. Proline has been obtained in relatively large amount 

 from a number of the plant proteins, and arginine is yielded in larger 

 proportion by many of them than by most animal proteins. The 

 proteins soluble in alcohol, on the other hand, yield these basic amino- 

 acids in remarkably small proportion, and, as Kossel and Kutscher 

 showed (205), are the only proteins, with the exception of the protamines, 

 which have yet been found to yield no lysine. It has long been re- 

 cognised that many vegetable proteins contain more nitrogen than the 

 animal proteins, and it has been recently shown (364) that this differ- 

 ence is chiefly caused by the relatively larger proportion of arginine 

 which most of the seed proteins yield. A few, however, of the seed 

 proteins which are rich in nitrogen yield but little arginine. In these 

 the high nitrogen content is due to a larger proportion of amide 

 nitrogen. 



