title: Phosphorylation of 40-S ribosomal subunits by cAMP-dependent, cGMP-dependent and protease-activated protein kinases.
abstract: The phosphorylation of 40-S ribosomal subunits by cyclic-nucleotide-dependent and protease-activated protein kinases from rabbit reticulocytes was studied in vitro. Under optimal conditions the cAMP-dependent protein kinases incorporated up to 2 mol phosphate/mol S6. The electrophoretic mobility of S6 following phosphorylation indicated that this value was not an average for a population of maximally phosphorylated and non-phosphorylated S6 but represented a uniform population of diphosphorylated 40-S ribosomal subunits. Tryptic digests of S6 were analyzed by two-dimensional fingerprinting following phosphorylation with the cAMP-dependent protein kinase; two phosphopeptides, A and B, were observed. When 40-S ribosomal subunits were examined with the cGMP-dependent protein kinase, 1 mol phosphate was incorporated/mol S6. Upon analysis of the phosphopeptides obtained with the cGMP-dependent protein kinase, only peptide A was observed. S6 was also modified by a cyclic-nucleotide-independent protein kinase, protease-activated kinase II, following activation of the enzyme by limited proteolytic digestion. These findings suggest that a multiple protein kinase system may regulate the phosphorylation state of S6. A second ribosomal protein, S10, was phosphorylated by a different cyclic-nucleotide-independent protein kinase, protease-activated kinase I, and up to 1 mol phosphate was incorporated.
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000494:pharmacology*; D006152:Cyclic GMP / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D010447:Peptide Hydrolases / Q000494:pharmacology*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology; D012269:Ribosomal Proteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D012269:Ribosomal Proteins; D015636:Magnesium Chloride; D000242:Cyclic AMP; D011494:Protein Kinases; D010447:Peptide Hydrolases; D006152:Cyclic GMP; D008274:Magnesium