Reversible dissociation of porcine ceruloplasmin into subunits

Abstract

Porcine ceruloplasmin is dissociated into two subunits of equal molecular weight at 4.5 M urea in the presence of p-chloromercuribenzoate. Removal of urea by dialysis results in the formation of a homogeneous reassociated component. The component, because it is identical to the native protein in respect to molecular weight, molar extinction coefficient at 610 mμm and oxidase activity, may be the ‘native’ protein. When the samples treated with increasing concentrations of urea are dialyzed, a new component (molecular weight, 500 000) is formed in an increasing amount, and the amount of native protein is decreased. Removal of urea from the 8 M urea-treated sample results in formation of only the aggregated component. The aggregated component is devoid of oxidase activity and of blue color. To a small degree the subunits are also reassociated into the native protein upon removal of urea by gel filtration.