title: Progesterone receptor subunits are high-affinity substrates for phosphorylation by epidermal growth factor receptor.
abstract: Purified preparations of epidermal growth factor (EGF) receptor were used to test hen oviduct progesterone receptor subunits as substrates for phosphorylation catalyzed by EGF receptor. Both the 80-kilodalton (kDa) (A) and the 105-kDa (B) progesterone receptor subunits were phosphorylated in a reaction that required EGF and EGF receptor. No phosphorylation of progesterone receptor subunits was observed in the absence of EGF receptor, even when Ca2+ was substituted for Mg2+ and Mn2+. Phospho amino acid analysis revealed phosphorylation at tyrosine residues, with no phosphorylation detectable at serine or threonine residues. Two-dimensional maps of phosphopeptides generated from phosphorylated 80- or 105-kDa subunits by tryptic digestion revealed similar patterns, with resolution of two major, several minor, and a number of very minor phosphopeptides. The Km of progesterone receptor for phosphorylation by EGF-activated EGF receptor was 100 nM and the Vmax was 2.5 nmol/min per mg of EGF receptor protein at 0 degrees C. The stoichiometry of phosphorylation/hormone binding for progesterone receptor subunits was 0.31 at ice-bath temperature and approximately 1.0 at 22 degrees C.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D066246:ErbB Receptors; D005260:Female; D046911:Macromolecular Substances; D010057:Oviducts; D010766:Phosphorylation; D019000:Phosphotyrosine; D011494:Protein Kinases / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D011956:Receptors, Cell Surface; D011980:Receptors, Progesterone; D019000:Phosphotyrosine; D014443:Tyrosine; D011494:Protein Kinases; D066246:ErbB Receptors