Interaction of Oxidized and Reduced Uteroglobin with Progesterone

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Abstract
Binding of added progesterone to native uteroglobin requires the reduction of the disulfide bonds that hold together the 2 polypeptide chains of the protein. The hypothesis that in the native oxidized state of uteroglobin the steroid binding cavity is preformed and occupied by a progesterone molecule was tested by several experimental means. Progesterone does not interact with oxidized uteroglobin, and the majority of the oxidized uteroglobin molecules purified from pseudopregnant rabbits do not contain a progesterone molecule. Oxidation of reduced uteroglobin in the presence of saturating amounts of progesterone does not result in significant retention of the steroid inside the oxidized protein.