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 S1- 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.