Cyclic AMP-dependent protein kinase phosphorylates rabbit reticulocyte elongation factor-2 kinase and induces calcium-independent activity.
The catalytic subunit of cyclic AMP-dependent protein kinase (PKA) phosphorylated purified calcium/calmodulin-dependent eukaryotic elongation factor-2 (eEF-2) kinase, isolated from rabbit reticulocyte lysates. It maximally incorporated about 1 mol of phosphate/mol of eEF-2 kinase. The Km of eEF-2 kinase for PKA was calculated to be 7 microM. Phosphorylation of eEF-2 kinase by PKA induced calcium-independent activity which amounted to 40-50% of the total activity measured in the presence of calcium. Furthermore, the level of calcium-independent activity induced by phosphorylation by PKA was similar to that induced by the calcium-stimulated autophosphorylation of eEF-2 kinase. Phosphopeptide mapping of eEF-2 kinase labelled by autophosphorylation and by PKA revealed a number of common phosphopeptides. This suggests that PKA may phosphorylate the same site(s) which are phosphorylated autocatalytically and which are responsible for the induction of calcium-independent activity. The possible implications these findings have for the control of translation are discussed.
Redpath
N T
NT
Department of Biochemistry, School of Medical Sciences, University of Bristol, U.K.
Proud
C G
CG
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002384:Catalysis; D004591:Electrophoresis, Polyacrylamide Gel; D054736:Elongation Factor 2 Kinase; D004789:Enzyme Activation; D010766:Phosphorylation; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology*
D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D054736:Elongation Factor 2 Kinase; D002118:Calcium