The vegetable proteins / by Thomas B. Osborne.

  • Osborne, Thomas B. (Thomas Burr), 1859-1929.
Date:
1924
Catalogue details

Licence: In copyright

Credit: The vegetable proteins / by Thomas B. Osborne. Source: Wellcome Collection.

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    closely related botanically, contain chemically identical proteins. At the present time the anaphylaxis reaction seems to be the best means available for establishing the probable chemical identity of protein preparations from different sources. The conclusion appears to be justified that an almost infinite number of chemically different proteins exist in plants and that it is a hopeless task to attempt to deal with any considerable part of these individually. It is, however, important to have a few well characterised individuals representing different types which shall afford material for studying the physical and chemical characters of this important group of substances. During the past thirty years the author and his associates have con- centrated attention on the preparation of a few proteins from different groups of seeds which in physical properties and chemical structure appear to present especial opportunities for future investigation. In this connection it is worth while to consider the evidence now available which indicates the possibility of separating these proteins from one another, as well as from associated substances, for it has been generally assumed that the difficulties presented in making such separa- tions are so great that there is little hope for success. Most of the seed proteins now known are soluble in salt solutions and can be precipitated by dialysis in the form of crystals or spheroids which are relatively large when compared with the minute particles of an amorphous precipitate. These separate from solution very slowly, and are deposited as dense precipitates which adsorb associated substances to a far less extent than do the amorphous, bulky precipitates of most proteins of animal origin. Good evidence of this is the fact that the chief protein of the castor bean, as Osborne, Mendel, and Harris have found, could be freed by a single reprecipitation by dialysis from all but minute traces of any toxic substance, though the solution from which it separated on the first dialysis contained a large quantity of the extremely poisonous ricin. Ricin, if not a protein, is, at least, so intimately associated with protein that it is almost quantitatively precipitated therewith. The conclusion is, therefore, justified that the separation from the water-soluble protein by a single reprecipitation by dialysis is in a high degree complete. This fact is good ground for considering it possible to separate proteins very completely from one another under such conditions. Further evidence of this is furnished also by the anaphylaxis reac- tion. As is well known, extremely small quantities of a protein suffice to sensitise guinea pigs to subsequent doses of the same protein. In many cases Wells and Osborne [1915] found that preparations of