Phosphorylation of 40‐S Ribosomal Subunits by cAMP‐Dependent, cGMP‐Dependent and Protease‐Activated Protein Kinases
Open Access
- 1 April 1982
- journal article
- Published by Wiley in European Journal of Biochemistry
- Vol. 123 (2), 421-428
- https://doi.org/10.1111/j.1432-1033.1982.tb19785.x
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.Keywords
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