Differential activation of two protease-activated protein kinases from reticulocytes by a Ca2+-stimulated protease and identification of phosphorylated translational components.
Two protein kinases have been partially purified from rabbit reticulocytes and shown to be activated by limited proteolysis with trypsin [S.M. Tahara and J.A. Traugh (1981) J. Biol. Chem. 256, 11558-11564; P.T. Tuazon, W.C. Merrick, and J.A. Traugh (1980) J. Biol. Chem. 255, 10954-10958]. Reticulocyte lysate was examined for protease activities which might be involved in activation of the protein kinases in vivo. Two neutral proteases, differentially activated by Fe2+ and Ca2+, were identified and partially purified. The Ca2+-stimulated protease specifically activated protease-activated kinase II; no effect was observed on protease-activated kinase I. The Fe2+-stimulated protease was not active on either protein kinase. The protease-activated kinases were examined using initiation factors (eIF) and 40-S ribosomal subunits as substrate. Protease-activated kinase I phosphorylated one subunit of eIF-3 (Mr 130000), eIF-4B and 40-S ribosomal protein S10. Protease-activated kinase II modified the beta subunit of eIF-2 (Mr 53000) and 40-S ribosomal protein S6. The substrate specificities are unique when compared with other cAMP-dependent and cAMP-independent protein kinases from reticulocytes.
D002118:Calcium / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D010447:Peptide Hydrolases / Q000494:pharmacology*; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000302:isolation & purification; D012156:Reticulocytes / Q000201:enzymology*
D012335:RNA, Ribosomal; D011494:Protein Kinases; D010447:Peptide Hydrolases; D002118:Calcium