A practical course of chemical physiology / by D. Noël Paton and Edward P. Cathcart.
- Diarmid Noel Paton
- Date:
- 1910
Licence: In copyright
Credit: A practical course of chemical physiology / by D. Noël Paton and Edward P. Cathcart. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
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![elements be absent, add ammonia to a large quantity of the acid solution. It should remain clear.] III. Decomposition Products of the Proteins. # Proteins on prolonged boiling with mineral acids (acid hydrolysis), or on prolonged digestion with proteolytic ferments, break down into products which no longer give the biuret reaction. 20 grins, casein are boiled with 100 c.c. 25 per cent, sulphuric acid for 10—12 hours. To 20 c.c. of this biuret free product, add 10 per cent, phosphotungstic acid in 5 per cent. H2S04 solution so long as a precipitate forms. When precipitation is complete, filter, best with the aid of a water pump, wash the precipitate with a small quantity of dilute phosphotungstic acid and then dry. The nitrogen in the precipitate and in the filtrate may be estimated by Kjeldahl’s method. By the above method the monamino are separated from the diamino acids. The monamino acids, the most important being glycocoll, alanin, leucin, tyrosin, are to be found in the filtrate. In the precipitate are found the diamino acids, arginin and lysin and the base histidin. [With ferment digestion, but not after acid hydrolysis, polypeptides are found. These polypeptides are condensa- tion products arising by the union of two or more amino acids. The simplest is glycyl-glycin from 2 mols. of glycocoll. The majority of polypeptides are precipitated by phosphotungstic acid.] Tryptophane also is found among the decomposition products. It is obtained from the digest by precipitation with mercuric salts. IV. EXAMINATION OF NUCLEO-PKOTEIN. Boil 100-200 grms. finely minced pancreas with about a litre of water for ten to fifteen minutes and then filter. To the filtrate, whilst still warm, add acetic acid drop by drop](https://iiif.wellcomecollection.org/image/b24932656_0088.jp2/full/800%2C/0/default.jpg)
