Observations on the crystallization of animal proteids / by F. Gowland Hopkins and S.N. Pinkus.

  • Hopkins, Frederick Gowland, Sir, 1861-1947.
Date:
[1898?]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the crystallization of animal proteids / by F. Gowland Hopkins and S.N. Pinkus. Source: Wellcome Collection.

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    amounts of acid, very minute additions of the salt will throw the proteid out of solution. It is of course well known that, in the presence of certain salts, acetic acid will precipitate albumens; but we believe it has not been observed in this connection how minute a quantity of ammonium sulphate will act as a precipitant of egg-albumen if acetic acid be first added in considerable quantity. Slight preliminary acidification of a solution will greatly reduce the quantity of salt necessary to precipitate it, and with increase of acid, within certain limits, the requisite amount of salt becomes less and less. The maximum influence of the acid is felt when about 30 °/0 HA is present; after this proportion is exceeded, more salt becomes necessary for precipitation as the acidity increases, though the amount remains enormously less than in the absence of acid. If to a one per cent, solution of egg-albumen sufficient glacial acetic acid be added for the solution to contain 30 °/0 of the latter, subsequent admixture with at most 0'4°/o of its bulk of saturated ammonium sulphate solution will produce visible precipitation, something like g-i^-th of the amount requisite when acid is absent. If it be mixed with 2 or 3 per cent, of its bulk of saturated ammonium sulphate solution pre¬ cipitation in such an acid mixture becomes very nearly complete. These facts have an important bearing upon any theory of the influence of salts upon proteid precipitation. For instance, whatever the pre¬ liminary effect of the strong acid upon the albumen, the acid solution by itself of course remains perfectly clear, and it is very unlikely that the minute proportion of ammonium sulphate subsequently producing precipitation could involve any dehydrating effect. For the purpose of this paper it is of chief interest to note that the precipitates produced by the small proportion of salt in the presence of a large amount of acid remain amorphous even on long standing; in marked contrast to those formed with a large proportion of salt and a very small proportion of acid, which, as we have shown, are obtained crystalline with extraordinary ease. Serum Albumen. When horses’ serum is mixed with saturated ammonium sulphate, as in Giirber’s process for the preparation of crystals of serum albumen, there is, as in the case of egg-white, an abundant production of free ammonia; and, as with the ovalbumen, we have found that neutralization of the free alkali with acetic acid greatly assists crystallization. Acidification does not it is true lead to such remarkably rapid results as may be obtained with the egg-proteid;