[Relation between surface denaturation of immunoglobulin G in monolayers and the pH of the solution]

Dependence of surface denaturation kinetics of rabbit immunoglobulin G (IgG) in monomolecular layers at air-water interfaces on the substrate pH has been studied. By measuring the surface potential the drift of the isoelectric point of IgG in monolayer as compared to that of the bulk aqueous phase in the direction of high pH values has been demonstrated. The IgG molecule displays the greatest stability in monolayer at the isoelectric point. An increase of protein molecules positive charge in the region of 7.5--5.5 pH units is not sufficient for prominent acceleration of surface denaturation in comparison to the isoelectric point. A decrease of the substrate pH lower than 5.5 units is followed by the growth of the rate of surface denaturation which is directly proportional to [H+] concentration in the substrate. In the same region of pH values compensation of charges of protein molecules takes place, so that the surface potential is not changed and does not depend on the rate of molecular denaturation. High conformational stability of IgG molecules in monomolecular layers at air water interface has been confirmed.