Characterization of linear polymers induced by thermal denaturation of ovalbumin

Abstract

The mechanism of formation and the characteristics of the linear ovalbumin aggregates induced by thermal denaturation of ovalbumin molecules were examined by gel permeation chromatography (GPC), light scattering and viscometry. Polymerization was initiated by thermal denaturation and, at 75°C, the denaturation was the rate-limiting step of the polymerization. The GPC elution time of aggregates depended on the heating conditions, that is, the higher the protein concentration and the longer the heating time, the larger the aggregates formed by heating. Oligomers of ovalbumin were detected only at a very early stage of the heat treatment. With increasing heating time the molecular weight distribution of the ovalbumin aggregates approached the most probable distribution, the M w/ M n ratio being close to 2, where M w and M n are the weight-and the number-average molecular weights respectively. The weight-average molecular weights of the linear polymers formed at 80°C (at 5 mg/ml) were found by light scattering to increase from 740 000 to 8 850 000 as heating time increased from 3 min to 24 h. Experimental values of the mean-square radius of gyration and intrinsic viscosity of the series of aggregates were corrected for the molecular weight distribution and analyzed in the light of dilute polymer solution theories. It was found that the ovalbumin linear aggregate may be described by the wormlike cylinder model with M L = 1.6 × 10 −3 Å −1, d = 120 Å and q = 230 Å, where M L, d and q are the molecular weight per unit contour length, diameter and persistence length respectively.