Pyridoxal phosphate extracts progesterone receptors from the nuclear fraction of hamster uterus. Optimal extraction occurs after 2 h at 2 C with 5 mM pyridoxal phosphate. At millimolar concentrations, pyridoxal phosphate also extracts non-receptor proteins from the nuclei, in amounts equivalent to those released by high salt (0.5 M KO) treatment (~10 mg protein per gram tissue). Thus, although pyridoxal phosphate is a useful probe for studying the interaction of steroid receptors with nuclear components, it does not selectively extract nuclear steroid receptors. The pyridoxal phosphate-extracted nuclear progesterone receptor had a sedimentation coefficient of 3.3S. Upon reduction with sodium borohydride, this species was converted to a 2.5S molecule. Sodium borohydride reduction of the pyridoxal phosphate-extracted nuclear receptor also caused a significant change in the steroid binding specificity of the molecule. The steroid specificity of the unreduced pyridoxal phosphate-extracted nuclear receptor was virtually identical to that of the KCl-extracted nuclear receptor. In contrast, deoxycorticosterone and 5α-pregnanedione competed 3- to 8-fold less effectively with progesterone for binding to the reduced form of pyridoxal phosphate-extracted nuclear receptor as compared to the other receptor forms.
ASJC Scopus subject areas