Licence: In copyright
Credit: The vegetable proteins / by Thomas B. Osborne. Source: Wellcome Collection.
![and Leavenworth [1921] as well as Chibnall and Schryver [1921] have undertaken to isolate such protein, the former from spinach leaves and green alfalfa plants, the latter from cabbage, bean, and spinach leaves. From these investigations it appears that only a small part of the protein of the clear, expressed juice is in true solution and that most of this is coagulated by adding alcohol or heating. Much the greater part of the protein in the leaf is insoluble in such solvents as are usually employed for extracting proteins. The majority of seed proteins thus far studied are soluble in neutral saline solutions from which they are precipitated by dilution or 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 protein precipitable by dialysis in forms similar to, or identical with, those which exist in the seed. Seeds of the cereals which contain the protein in a finely granular condition and without definite form yield relatively small quantities soluble in saline solutions. The proteins isolated from many seeds are apparently ob- tained with unchanged properties. The crystalline and spheroidal forms exhibited by these proteins within the cells can be artificially reproduced by dialysing their saline solutions. In those cells of the endosperm in which protein is most frequently found in the form of crystals, or of small spheres, there is usually observed a globule, composed largely of insoluble mineral substance, commonly called a globoid. This globoid is formed from soluble mineral salts contained in the fluid of the cell, and it is possible that, as its constituents pass out of solution, through the formation of an insoluble combination, the concentration of the salts in the cell fluid is correspondingly reduced and the protein thereby precipitated, in much the same way as occurs when salts are removed by dialysis. As already stated, the proteins extracted from seeds are obtained in various forms which represent distinctly different protein substances. The solubility of the protein matter in different seeds varies greatly, but in general it is found that a part is soluble in water, a part is soluble in neutral saline solutions and a part is insoluble in either of these solutions but soluble in dilute solutions of acids or alkalis, while in the seeds of the cereals a part is also soluble in alcohol of from 70 to 90 per cent. The proteins extracted from seeds by these several solvents will be considered in greater detail later.](https://iiif.wellcomecollection.org/image/b29807670_0032.jp2/full/800%2C/0/default.jpg)
