Physicochemical and Functional Properties of Hen Ovalbumin Dephosphorylated by Acid Phosphatase

Abstract

Hen egg ovalbumin is a mixture of three kinds of proteins, A1, A2, and A3 with two, one, and no phosphoryl residues, respectively. These three proteins were obtained by acid phosphatase treatment and then chromatography on a DEAE cellulofine AH column. The isoelectric points of A1, A2, and A3 were found by isoelectric focusing to be pH 4.75, 4.89, and 4.94, respectively. The denaturation temperature of each protein was examined by differential scanning calorimetry at its own isoelectric point and at pH 4.65. At both pHs, A3 had a lower denaturation temperature than A2 or A1. The surface tension of an A3 solution reached a constant more quickly than A1 or A2 after formation of a new surface of the solution. These results indicate that the completely dephosphorylated ovalbumin A3 is more susceptible to heat and surface denaturation than phosphorylated ovalbumin is. The difference in the heat aggregation patterns of A1, A2, and A3 solutions at different pH or salt concentrations showed that the electrostatic-repulsive force is important in helping to prevent the random aggregation of denatured ovalbumin.