Interaction of Uteroglobin With Progesterone, 5αPregnane-3,20-Dione and Estrogens

Publisher Website
Google Scholar
Abstract
Uteroglobin was obtained from 5 day pregnant rabbits and purified to homogeneity by Sephadex G 75 and DEAE-cellulose chromatographies. Progesterone binding to uteroglobin was decreased by lyophilization and enhanced by SH-reducing agents. Dithiothreitol was more effective than dithioerythritol, and .beta.-mercaptoethanol was only active at 25 to 100 mM concentrations. SH-blocking agents (iodoacetate, iodoacetamide, p-hydroxymercuribenzoate and dithiobisnitrobenzoic acid) inhibited binding. In the absence of SH-reducing agents only 1 in every 500 uteroglobin molecules bound the hormone, whereas under optimal conditions (20 mM dithiothreitol) 1 in every 2 molecules bound progesterone. There was no significant difference in equilibrium dissociation constants under these 2 conditions. Uteroglobin had a relatively high affinity for progesterone (Kd = 4.1 .times. 10-7 M) but a 3-fold higher affinity for 5.alpha.-pregnane-3,20-dione (Kd = 1.3 .times. 10-7 M). Estradiol was bound but non-specifically with a very low affinity, and its binding was not enhanced by SH-reducing agents. Hormonal specificity of binding to uteroglobin was different from that of binding to rabbit uterine progesterone receptor. Various synthetic progestagens (chlormadinone acetate, norethisterone, R5020) were bound to the latter but not to the former protein. Diethylstilbestrol had some affinity (15% of that of progesterone) for uteroglobin and no affinity for the progesterone receptor. Uteroglobin incubated in the presence or absence of cofactors (NADH and NADPH) with or without dithiothreitol did not metabolize progesterone.