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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    sulphate at very different degrees of saturation. Although many of them are precipitated by adding an equal volume of a saturated solution of ammonium sulphate to their solutions, others are not precipitated until their solutions are nearly saturated with this salt. The animal globulins are all coagulated by heating their solutions to various temperatures. Most of the seed globulins are only im- perfectly coagulated by heating their solutions even to boiling, and some of them can be thus heated for a very long time without showing any apparent change. A number of the vegetable globulins can be readily obtained in crystals; some of them crystallise with difficulty, and nearly all of those which do not crystallise are obtained in the form of minute spheroids. Crystallisation can be effected in various ways. Globulins which crystallise readily are usually precipitated by dialysis in well- formed crystals. Such are edestin from the hemp-seed, excelsin from the Brazil-nut, and the globulins of the squash-seed, the flax-seed, the oat-kernel and the castor bean. The globulin of the castor-bean is commonly obtained by dialysis in the form of spheroids, but frequently mixtures of spheroids and crystals result, although occasionally completely crystalline separations occur. Phaseolin, from Phaseolus vulgaris, frequently precipitates on dialysis in the form of minute spheroids, mixed with a few octahedral crystals which sometimes are of unusual size and very perfect form, but completely crystalline preparations of this globulin have never yet been obtained. Globulins which crystallise easily generally can be obtained in crystals by diluting their sodium chloride solutions with water heated to 50° or 6o° until a slight turbidity forms. After warming the diluted solution until this turbidity disappears and then allowing it to cool slowly, the protein separates in well-developed crystals. Schmiedeberg [1877] who obtained crystals of the globulin from the Brazil-nut, by treating its solution with magnesia and evaporating it slowly, considered the crystals of this substance to be the mag- nesium salt of the protein. This view of the nature of the crystals of this globulin was formerly accepted, and was frequently found in the current literature dealing with this protein, although Osborne [1892, 3], showed that much more perfectly crystalline preparations of this globulin than are described by Schmiedeberg are obtained by simply dialysing its faintly acid saline solutions in running water. These crystals are unquestionably salts of the globulin with the acid of the extract, and are not compounds with magnesia or any other base.