The vegetable proteins / by Thomas B. Osborne.

  • Osborne, Thomas B. (Thomas Burr), 1859-1929.
Date:
1924
Catalogue details

Licence: In copyright

Credit: The vegetable proteins / by Thomas B. Osborne. Source: Wellcome Collection.

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    CHAPTER V. THE RELATION OF PROTEINS TO ACIDS AND BASES. By L. J. Henderson, Ph.D., Sc.D. In their relations with acids and bases, proteins behave as if there were present in the molecule a considerable number of acid radicals of various degrees of strength, and a considerable number of similar basic radicals. In solutions which are sufficiently acid these basic radicals must be completely combined with acid, and the acid radicals must be completely free. On the other hand, in sufficiently alkaline solutions the acid radicles must be completely combined with bases, and the basic radicals must be completely free. Accordingly, it is apparent that there must be a reaction, or a zone, between the state of complete combination with acid and that of complete combination with base, in which there is no combination either with acid or with base, or else in which such combination is a minimum. In particular, there must be a point at which the ionisation of the protein through its acid radicals and that through its basic radicals are ec[ual. As a first approximation this may be considered the isoelectric point, for under these circumstances the protein will move neither to the anode nor to the cathode. At this point and in its neighbourhood the solubility is likely to be a minimum, for in the case of proteins [Cohn, 1922] it is probably the undissociated molecule which chiefly determines solubility, the ions being relatively soluble substances. The isoelectric point or zone may fall at an acid, neutral, or alkaline reaction, according to the relative number and strength of the acid and basic groups of the molecule. Thus, if the acid groups be numerous and strong, and the basic groups less numerous and weak, it is evident that the isoelectric state must occur at an acid reaction. Moreover, in case both acid and basic radicals are all weak, there will be a wide zone of reaction throughout which the protein will be very slightly combined with either acid or base, and within which, as a first approximation, it