title: The regulation of ribosomal protein S-6 phosphorylation in Xenopus oocytes: a potential role for intracellular pH.
abstract: The intracellular pH of full-grown Xenopus oocytes increases from 7.2 to 7.6 in response to progesterone stimulation. Phosphorylation of the 40 S ribosomal protein S-6 increases six- to eightfold in these stimulated cells and this phosphorylation coincides with the intracellular alkalization. This is followed by a two- to threefold increase in the protein synthetic rate. Progesterone-treated cells cultured in choline chloride substituted Na-free medium fail to alkalize and S-6 is not phosphorylated. Weak bases, such as trimethylamine, methylamine, and procaine, artificially alkalize the cell cytoplasm and stimulate S-6 phosphorylation in medium containing or lacking sodium. The methylxanthine theophylline, suppresses S-6 phosphorylation and inhibits protein synthesis. This inhibition does not appear to involve cAMP. Rather, theophylline acidifies the oocyte cytoplasm. Thus, S-6 phosphorylation appears to be regulated by the intracellular pH of the cell. In addition, the level of protein synthesis in the oocyte seems to be correlated with the level of S-6 phosphorylation.
mesh_terms: D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011374:Progesterone / Q000494:pharmacology; D014176:Protein Biosynthesis; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins / Q000378:metabolism*; D013806:Theophylline / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D010750:Phosphoproteins; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D011374:Progesterone; D013806:Theophylline