STABILIZATION OF THE AVIAN PROGESTERONE RECEPTOR BY INHIBITORS

The avian progesterone receptor is known to be very temperature-labile; its hormone binding activity is lost within minutes at 37°C. However, when the receptor is first treated with pyridoxal 5'-phosphate, in the presence of sodium borohydride, the receptor is stabilized dramatically and can be incubated for up to 2 h at 37°C without loss of activity. Pyridoxal 5'-phosphate is known to block the binding of receptor to ATP-Sepharose, apparently by a Schiff base interaction with the receptor. Other such inhibitors were also tested for any stabilizing effect. Two of these, o-phenanthroline and aurintricarboxylic acid, decreased the stability of the receptor, while a very significant stabilization was observed after treatment with sodium molybdate. In addition to this effect, sodium molybdate appears to block activation or transformation of the progesterone receptor to the form which is able to bind to ATP-Sepharose. Once the receptor is in this activated form, sodium molybdate is no longer inhibitory whereas pyridoxal 5'-phosphate is still a potent inhibitor of ATP-Sepharose binding. These results indicate that the two stabilizing agents act through different mechanisms. © 1979.