The pH Stability Region of Proteins and Osmotic Swelling

Abstract

THE swelling of protein gels and tissues under the influence of acid or alkali is due mainly to osmotic forces set up on account of salt formation between the protein and the acid or base. Osmotic swelling always shows two well-marked maxima, one in the acid and one in the alkaline range, and it has generally been taken for granted that the pH-swelling curve should also show a sharply marked minimum corresponding to the iso-electric point of the protein. This misconception has arisen from the fact that the bulk of the work on the swelling and osmotic pressure of proteins has been done on gelatin and albumin, both of which show sharply marked minima, and where it is not unreasonable to assume that the protein molecules are present without any orientation.