Volume 1
The chemical constitution of the proteins / by R.H.A. Plimmer.
- Robert Plimmer
- Date:
- 1912-1913
Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
Credit: The chemical constitution of the proteins / by R.H.A. Plimmer. Source: Wellcome Collection.
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![when the water is removed by evaporation in vacuo. Phelps and Tillotson’s method seems to be preferable. 5. Separation of Glycine Rster Hydrochloride,—The glycine is never completely isolated as ester hydrochloride; the remainder is obtained as ester. 6. Extraction of Esters.—Loss always occurs in this part of the pro- cess, but is covered when the process is repeated. The loss is largely mechanical and cannot be avoided. A small quantity of organic matter is retained by the sodium sulphate used for drying the esters. 7. Distillation of Esters.—{a) In distilling off the ether, especially if its volume be large, a considerable quantity of esters distils at the same time. Two receivers should be used and the esters extracted from the distillate. ip) Decomposition of the esters occurs during the distillation, and a more or less large residue represents the loss. The products can be recovered, if necessary. Abderhalden has found that in the process up to this stage 25 per cent, of glutamic acid and 40 per cent, of aspartic acid are lost; some of the glutamic acid is lost by conversion into pyrrolidone carboxylic acid. The loss is greatly diminished if the distillation of fraction IV. be omitted. Osborne and Jones find that the separation of the esters in this fraction is not more troublesome than when they are distilled. 8. Separation of the Individual Amino Acids.—The greatest loss occurs here as none of the methods of isolating the compounds are perfect. (a) Proline.—The quantity extracted by alcohol is much greater than that obtained in a pure crystalline state and reckoned as proline. Estimation by Van Slyke’s method gives the actuaL amount. (p) Valine, Leucine, Isoleucine.—The figures given represent the quantity of substance isolated in a pure state. The leucine figures are really those for leucine + isoleucine. {c) Glycine and Alanine.—Nearly all the glycine can be obtained, but the actual amount of alanine is much greater. [d] Glutamic Acid.—Probably the figures given for this amino acid most nearly approach the real content of the protein in this constituent. (f) Aspartic Acid and Serine.—The figures are much too'low, as the method of separation is extremely unsatisfactory^](https://iiif.wellcomecollection.org/image/b28123219_0001_0058.jp2/full/800%2C/0/default.jpg)
