Behavior of S₁- and S₂-ovalbumin and S-ovalbumin A₁ in urea solution: Kinetics and equilibria

The isolation of S-, S₁-, and S₂-ovalbumin from domestic hen egg R-ovalbumin and of two methods for S-ovalbumin A₁ are described. The first is by heat treatment of R-ovalbumin A₁ and the second is of R-ovalbumin followed by fractionation on Sepharose. A kinetics and equilibrium study is made of their behavior in the presence of urea and compared with that of R-ovalbumins. As anticipated, the S-ovalbumins are much more resistant to urea than R-ovalbumins. Unlike the latter, S-ovalbumins' equilibrium profiles have a simpler sigmoidal shape. The unfolding of S ₁- and S₂-ovalbumin is an order of magnitude slower than that of R-ovalbumin. Some possible structural differences between R- and S-ovalbumin forms and their significance are discussed.