The physical chemistry of the proteins / by T. Brailsford Robertson.

  • Thorburn Robertson
Date:
1918
Catalogue details

Licence: In copyright

Credit: The physical chemistry of the proteins / by T. Brailsford Robertson. Source: Wellcome Collection.

    28/508 page 8
    3. The Connection between the Amino-Acid Content and the Properties of the Proteins. — The various proteins are found to be built up of the several units enumerated above together, possibly, with units which we have not yet succeeded in isolating. Some of the proteins are built up out of all of these units in vary- ing proportions, others out of a lesser number, so that in some cases amino-acids which are predominant among the products of the hydrolysis of one protein are absent from among the prod- ucts of the hydrolysis of another. Nevertheless the general relationship of the various units and their occurrence in dif- ferent proportions in the various proteins accounts not only for the differences, but also for the similarity between them. In many instances a definite parallelism can be traced between the chemical and physical behavior of the proteins and their amino-acid content. Thus the albumins, which are soluble in distilled water and are not coagulated by half-saturation of their solutions with ammonium sulphate, contain no glycin, while the globulins which are (when uncombined with bases or acids) insoluble in distilled water, and are coagulated by half-saturation of their solutions with ammonium sulphate, do contain this amino-acid. The alcohol-soluble vegetable proteins contain only a trace (probably attributable to associated impurities) of glycin and some of thenTcontain no lysin, their content of diamino-acids is very small, while their content of glutamic acid and of prolin is very high. The phosphoproteins (casein, vitellin) are also rather high in glutamic acid. Gelatin is characterized by its high glycin content and keratin (the protein of hair and feathers) by its high cystin content. The histones, which are predomi- nantly basic substances, contain about 30 per cent of diamino- acids, while the protamins, which are still more predominantly basic, contain only small amounts of monoamino-acids, sal- min containing over 80 per cent of arginin, while sturin con- tains 67 per cent of its nitrogen as arginin, 10 per cent in the form of histidin and from 6 to 7 per cent in the form of lysin (41). Kossel (35) has expressed the view that all proteins are built up around a protamin nucleus and that this accounts for the fact that the majority of the proteins yield, on hydrolysis, a certain proportion of diamino-acids.
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