On the pH at the surface of ovalbumin molecules, and the protein error with indicators

Abstract

PHs, the pH at the surface of a protein molecule, may be calculated from the Gibbs-Donnan equilibrium, or from the electrokinetic potential. For ovalbumin the 2 methods give results in reasonable agreement. The major part of the influence of neutral salt on the titration curve of ovalbumin is due to changes in pH, produced by the neutral salt. Part of the "protein error" with indicators is due to adsorbed indicator having the colour corresponding to pHs, and not that corresponding to the bulk pH. It is suggested that pHs is the significant pH in enzyme activity, and that enzyme activities should be detd. in buffers of constant ionic strength.