io THE VEGETABLE PROTEINS 



physiologically active tissues of the parent plant similar to that which 

 the animal albuminoids bear to the physiologically active tissues of the 

 animal, for the reserve protein of ripe seeds has even less connection 

 with the living tissues of the plant which produced it than the albumin- 

 oids of hair, horn and hoof have with the living tissues of the animal. 



This physiological analogy extends, within certain limits, to the 

 chemical characteristics of these substances. Like the animal al- 

 buminoids, the reserve seed proteins are more stable toward chemical 

 and physical agents than are the proteins which form parts of the living 

 substance of animals, and also, like most of the albuminoids, they differ 

 more widely in the proportion of some one or more of the amino-acids 

 which they yield when hydrolysed than do the more physiologically 

 active proteins of either vegetable or animal origin, the protamines 

 excepted. Thus gliadin of wheat and hordein of barley yield approxi- 

 mately 37 per cent, of glutaminic acid, while silk fibroin yields 36 per 

 cent, of glycocoll and 21 per cent of alanine. The alcohol-soluble 

 seed proteins yield the basic amino-acids in very small amount as do 

 also some of the albuminoids, e.g., elastin and keratin. No such wide 

 differences have been found among the physiologically active proteins 

 of plants or animals, and in this respect many seed proteins and al- 

 buminoids present a marked structural difference from the tissue pro- 

 teins. The seed proteins, moreover, offer an advantage for chemical 

 study which most of the albuminoids do not, as, unlike most of the 

 latter, they can be obtained in a soluble form and very frequently in 

 a well-crystallised state which makes their purification much easier 

 than that of the insoluble albuminoids. 



Owing to their relatively great stability most of the seed proteins 

 can be readily subjected to extensive fractional precipitation, and the 

 chemical and physical properties of successive fractions can be easily 

 compared. These proteins, therefore, yield more definite and well- 

 characterised preparations than do most of the known proteins of 

 animal origin, and it is expected that a study of them will result in 

 more definite knowledge of the chemistry of protein matter than can 

 be obtained by a study of proteins from any other source. 



The majority of seed proteins thus far studied are globulins, that is, 

 they are soluble in neutral saline solutions from which they are pre- 

 cipitated by dilution or by dialysis. Those seeds, as yet studied, in 

 which the protein occurs within the cell in the form of crystals or 

 spheroids or of partly crystalline masses yield large quantities of 

 globulin precipitable by dialysis in forms similar to, or identical with, 

 those which exist in the seed. Seeds of the cereals which contain the 



