Differing effects of the protein phosphatase inhibitors okadaic acid and microcystin on translation in reticulocyte lysates.
The effects of the cyanobacterial toxin and protein phosphatase inhibitor, microcystin, on translation in rabbit reticulocyte lysates have been studied. Microcystin inhibited translation with similar potency to the protein phosphatase inhibitor okadaic acid. Unlike low concentrations of okadaic acid, however, it inhibited both the initiation and elongation stages. This was demonstrated using EGTA to inhibit the phosphorylation and inactivation of elongation factor eEF-2. A method for detecting changes in eEF-2 phosphorylation was developed. eEF-2 was found to exist as three different species: eEF-2 was largely monophosphorylated in reticulocyte lysates under control conditions, the remainder being unphosphorylated. Okadaic acid and microcystin increased the level of the bisphosphorylated species. The implications of multiple phosphorylation of eEF-2 for the control of translation is discussed. Microcystin was also found to increase the phosphorylation of eIF-2 alpha (and therefore to inhibit initiation) at lower concentrations than okadaic acid, suggesting that the major eIF-2 alpha phosphatase in the reticulocyte lysate is phosphatase-1.
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Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, U.K.
Proud
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D000818:Animals; D002458:Cell Fractionation; D004533:Egtazic Acid / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000494:pharmacology*; D015151:Immunoblotting; D007930:Leucine / Q000378:metabolism; D008387:Marine Toxins; D052998:Microcystins; D019319:Okadaic Acid; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors / Q000378:metabolism / Q000494:pharmacology; D010448:Peptide Initiation Factors / Q000378:metabolism / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation; D039881:Prokaryotic Initiation Factor-2; D014176:Protein Biosynthesis / Q000187:drug effects*; D054645:Protein Phosphatase 1; D011817:Rabbits; D012156:Reticulocytes / Q000187:drug effects / Q000378:metabolism
D004988:Ethers, Cyclic; D008387:Marine Toxins; D052998:Microcystins; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors; D010448:Peptide Initiation Factors; D010456:Peptides, Cyclic; D039881:Prokaryotic Initiation Factor-2; D019319:Okadaic Acid; D004533:Egtazic Acid; C063855:microcystin RR; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D007930:Leucine