title: pH-dependent effects of sodium tungstate on the steroid-binding properties of the hen oviduct progesterone receptor.
abstract: Effects of sodium tungstate on the steroid-binding properties of hen oviduct progesterone receptor were examined and were found to be pH-dependent. When freshly prepared hen oviduct cytosol containing progesterone receptor was heated at 37 degrees C for 20 min, its ability to bind [3H]progesterone decreased to 20% level of unheated samples. At pH 7, presence of 2-3 mM tungstate during the above incubation period reduced this loss of binding. At higher tungstate concentrations (greater than 5 mM), this stabilizing effect was gradually abolished. Similar results were obtained with preparations that contained [3H]progesterone-receptor complexes; 70-80% of which remained after a 20 min incubation at 37 degrees C in the presence of 2-3 mM tungstate at pH 7. At pH 8, presence of tungstate (1-10 mM) during the 37 degrees C incubation stabilized both the steroid-bound and the unoccupied progesterone receptor in a concentration-dependent manner. The extent of steroid binding by the receptor at 4 degrees C remained unchanged in the presence of up to 10 mM tungstate at both pH 7 and pH 8 assay conditions while presence of 20 mM tungstate lowered this binding capacity. These results indicate that tungstate effects may be mediated via its interaction with the progesterone receptor.
mesh_terms: D000818:Animals; D002645:Chickens; D003600:Cytosol / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010057:Oviducts / Q000378:metabolism*; D011374:Progesterone / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000187:drug effects / Q000378:metabolism*; D014414:Tungsten / Q000494:pharmacology*; D017973:Tungsten Compounds
chemical_list: D011980:Receptors, Progesterone; D017973:Tungsten Compounds; D011374:Progesterone; C025399:sodium tungstate(VI); D014414:Tungsten