Activity of protein phosphatases against initiation factor-2 and elongation factor-2.
The protein phosphatases active against phosphorylase a, elongation factor-2 (EF-2) and the alpha-subunit of initiation factor-2 (eIF-2) [eIF-2(alpha P)] were studied in extracts of rabbit reticulocytes. Swiss-mouse 3T3 fibroblasts and rat hepatocytes, by use of the specific phosphatase inhibitors okadaic acid and inhibitor proteins-1 and -2. In all three extracts tested, both phosphatase-1 and phosphatase-2A contributed to overall phosphatase activity against phosphorylase and eIF-2(alpha P), but phosphatase-2B and -2C did not. In contrast, only protein phosphatase-2A was active against EF-2. Furthermore, in hepatocytes there was substantial type-2C phosphatase activity against EF-2, but not against phosphorylase or eIF-2 alpha. These findings in cell extracts were borne out by data obtained by studying the activities of purified protein phosphatase-1 and -2A against eIF-2(alpha P) and eIF-2(alpha P) was a moderately good substrate for both enzymes (relative to phosphorylase a). In contrast, EF-2 was a very poor substrate for protein phosphatase-1, but was dephosphorylated faster than phosphorylase a by protein phosphatase-2A. The implications of these findings for the control of translation and their relationships to previous work are discussed.
Redpath
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NT
Department of Biochemistry, School of Medical Sciences, University of Bristol, U.K.
Proud
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CG
D000818:Animals; D002478:Cells, Cultured; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D051379:Mice; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010762:Phosphorylase a / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D051381:Rats; D011919:Rats, Inbred Strains; D012156:Reticulocytes / Q000378:metabolism
D015852:Eukaryotic Initiation Factor-2; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors; D010762:Phosphorylase a; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2