Volume 1

The chemical constitution of the proteins / by R.H.A. Plimmer.

  • Plimmer, Robert Henry Aders, 1877-1955.
Date:
1912-1913
Catalogue details

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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    than it has hitherto been. Their preparation was no doubt due to the possibility of the presence of other units than those above described, which possibility will not be excluded until the quantity of products isolated reaches lOO per cent. The amino acids composing the protein molecule are generally referred to as the bricks, or foundation-stones, “ Bau-steine ” ; but as the English translation of the German word is not entirely expressive of its meaning, it is preferable to use the term unit or element for these compounds in their relation to the proteins. The methods which have been employed for the purpose of de- termining the composition of the protein molecule have been many and various. They may be classified under four headings :— (1) Fusion with alkali. (2) Oxidation with permanganate, chromic acid, etc. (3) Action of halogens. (4) Hydrolysis. Of these, the last, that of hydrolysis, has thrown most light on the darkness of this complex problem. Hydrolysis has been effected by the action of acids, of alkalies, and of the various proteoclastic enzymes which occur in plants and animals, and is practically the only method by which we have attained to our present knowledge. Proteins were first hydrolysed by acids in 1820 by Braconnot, who used dilute sul- phuric acid; between 1850 and 1875 hydrochloric acid was most fre- quently employed as the hydrolysing agent by Ritthausen, Hlasiwetz and Habermann and others, and from 1870 to 1880 Schiitzenberger employed baryta water under pressure. The action of vegetable enzymes on proteins has been studied chiefly by Schulze and his co- workers, that of animal enzymes by Kiihne, Kossel, Kutscher, Drechsel, and numerous other investigators. As the result of hydrolysis a complex mixture of all, or nearly all, the previously mentioned units is obtained. These have been isolated by various methods based upon the fractional crystallisation of the compounds themselves, or of their copper, silver, and other salts. Only when one or more of the amino acids occurred in somewhat large amounts was their isolation and characterisation effected; their amount seldom reached a value higher than 20 per cent, of the total quantity, and the remainder was represented by uncrystallisable syrups of un- known nature. The products described by Schiitzenberger have been shown by Hugounenq, GaHmard and Morel to be mixtures of now definitely known substances.