A practical course of chemical physiology / by D. Noël Paton and Edward P. Cathcart.

  • Diarmid Noel Paton
Date:
1910
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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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    (3) Filter these off, and to the filtrate apply the biuret test, and, if proteins are still present, add an equal volume of saturated (NH4)2S04 solution. Precipitate = Primary Proteoses (Proto- and Heteroproteoses). (There may be a precipitate of polysaccharides at this stage, see p. 14.) (4) Filter off these primary Proteoses, and if the filtrate give the biuret test, add solid (NH4)2S04 to full saturation. Precipitate = Secondary Proteose (Deuteroproteose, or Gelatin, see p. 11). (To separate these, filter and then dissolve the precipitate from the filter paper in water, and add solid MgS04 to full saturation. Precipitate = Gelatin.) (5) Filter, and apply biuret or xanthoproteic tests to the filtrate. A reaction indicates the presence of Peptone. II. Proteins not occurring in solution. Fibrin, Gluten, Coagulated Native Proteins, etc. These give the xanthoproteic test if simply suspended in water, and they may be generally recognised by their physical characters. B. Conjugated Proteins. Proteins linked to other bodies. 1. GlycoProteins (linked with carbohydrate).—(Use Saliva.) Mucin.—(1) Forms a viscous solution. (2) Precipitated by acetic acid and not soluble in excess. (3) Boiled with a mineral acid yields a sugar. (For test see p. 13.) 2. Nucleo-Proteins (linked with the phosphorus-con- taining nucleic acid).—(Use Bile.) These bodies are the chief constituents of cell nuclei. They are generally not precipitated on boiling, and behave much like the protoproteoses, but are soluble in alkalies and are thrown down on acidifying with acetic acid. They are redissolved in excess of acetic acid, thus differing from Mucin (vide supra). They yield phosphoric acid and purins •on boiling with a mineral acid.