The Ionization of Adsorbed Protein.

Abstract

The electric mobility of freely dispersed egg albumin and of microscopic quartz particles covered with the same protein have been shown to be fairly similar between pH 3.2 and 5.5. 1 Zetapotential measurements by the method of streaming potentials have confirmed this relationship. 2 The mobilities of quartz and other kinds of particles covered with egg albumin and with gelatin have since then been studied in the pH range noted in conjunction with the titration curves for these proteins. Under certain conditions, the change in mobility of the protein covered particles has been found to follow the titration curves of these proteins very closely. (Fig. 1.)

All of these observations indicate that the process of adsorption of the proteins mentioned does not appreciably change the ionization of the adsorbed protein at the protein-water interface. The free amino and carboxyl groups of the protein are, therefore, not primarily involved in the quartz-protein combination. These facts lend a particular biologic importance to the rôle of protein activity at phase boundaries. In this connection a striking example observed by Michaells and by Nelson and Griffin 3 demonstrates how an enzyme, invertase, although adsorbed at an inert phase boundary, may still retain its complete activity.