pH-dependent effects of sodium tungstate on the steroid-binding properties of hen oviduct progesterone receptor

Department of Biological Sciences, Oakland University, Rochester, MI 48063 U.S.A.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 12/1982; 719(2):267-72. DOI: 10.1016/0304-4165(82)90098-8
Source: PubMed


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.

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