The epsilon-amino groups of ovalbumin were modified with succinic anhydride; as many as 16 lysine residues were succinylated (3-carboxypropionylated). The five succinylated derivatives thus prepared were homogeneous with respect to the extent of chemical modification as shown by electrophoretic and immunological data. Succinylation of the amino groups altered electrophoretic mobility and isoionic pH of ovalbumin in the expected direction. U.v.-absorption and fluorescence spectra suggested changes in the microenvironment of the chromophores in the modified proteins. The difference-spectral results showed greater exposure of tyrosine and tryptophan residues in the succinylated ovalbumin. Increase in susceptibility to tryptic digestion, Stokes radius and intrinsic viscosity of native ovalbumin, which was observed on successive increase in the chemical modification, demonstrated a conformational change that was proportional to the extent of modification. The loss of immunological reactivity caused by chemical modification also indicated a conformational change in succinylated ovalbumin. The fact that the intrinsic viscosity of maximally modified ovalbumin was less than one-third of that for the completely denatured protein in 6M-guanidinium chloride suggested that the modified protein contained significant residual native structure. The latter presumably accommodates some antigenic determinants accounting for 37% residual immunological activity observed with maximally succinylated ovalbumin.

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