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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![extracted with cold absolute alcohol, and this operation is continued until all the insoluble amino acids are removed. The final alcoholic solution is evaporated to dryness and the residue weighed. As thus obtained, the proline is a mixture of the optically active and the racemic forms. These are separated by conversion into their copper salts by boiling with freshly precipitated copper oxide. The resulting dark-blue solution is evaporated to dryness, and the re- sidue is treated with absolute alcohol which dissolves the copper salt of the optically active proline. This solution on concentration yields the greater part of the compound in a crystalline state, but the remain- der is amorphous. The copper salt of the racemic proline, which is insoluble in alcohol, is purified by crystallisation from water. The identity of the compounds is established by a determination of the water of crystallisation and of the copper. The racemic copper salt contains 2 molecules of water of crystallisation, and in this state it is dark blue in colour; in the anhydrous state its colour is violet. Further characterisation is obtained by preparing proline from it. The copper salt is dissolved in water and decomposed with hydrogen sul- phide. The filtrate is concentrated to a small volume and precipitated with alcohol. The product, crystallised from alcohol, is obtained in flat needles, /-proline has a sweet taste, melts at 206-209° C. and has a rotation of [a]®^ = -77-4°. The amount of proline in the protein is given by the yield of the two copper salts obtained in a pure state. The actual proline content of the protein is considerably larger than the figures given in the tables (pp. 53-62). The real proline content can be accurately determined, as Van Slyke has shown by his nitrous acid method (p. 69), by a determina- tion of the total and amino-nitrogen of the product soluble in absolute alcohol. The alcoholic solution is made up to a definite volume and aliquot portions are taken for these estimations. The difference gives the amount of nitrogen present as proline from which the amount of proline can be calculated. In the case of caseinogen the proline con- tent was found to be 67 per cent, a figure which is twice that found by Abderhalden. It agrees with that found by Engeland by his method of methylation (p. 43).](https://iiif.wellcomecollection.org/image/b28123219_0001_0041.jp2/full/800%2C/0/default.jpg)
