title: Dephosphorylation of synthetic phosphopeptides by protein phosphatase-T, a phosphothreonyl protein phosphatase.
abstract: The synthetic phosphohexapeptides Arg-Arg-Ala-Thr(35P)-Val-Ala and Arg-Arg-Ala-Ser(32P)-Val-Ala, phosphorylated by the cAMP-dependent protein kinase and differing only in the nature of the phosphorylated residue, have been used as substrates of a partially purified rat liver protein phosphatase-T, distinct from the multifunctional protein phosphatase-1. While the phosphothreonyl hexapeptide is readily dephosphorylated (exhibiting a Km = 15 microM), the phosphoseryl one is almost unaffected. Such a behavior is not shared by protein phosphatase-1, calf intestine alkaline phosphatase, and potato acid phosphatase, all of which are more active on the phosphoseryl hexapeptide. The NH2-terminal basic residues critical for cAMP-dependent phosphorylation are not required in the dephosphorylation reaction, as both Arg can be removed without impairing the efficiency of protein phosphatase-T toward the phosphothreonyl peptide. On the other hand, the replacement of 2 Pro for the Ala and Val flanking Thr(32P), to give a new phosphohexapeptide reproducing the phosphorylated site of protein phosphatase inhibitor-1, prevents the protein phosphatase-T activity. Moreover, IgG heavy chain 32P labeled in tyrosine is not affected by protein phosphatase-T, while it is dephosphorylated by alkaline phosphatase. These results would indicate that protein phosphatase(s)-T represent a distinct class of protein phosphatases specifically involved in the dephosphorylation of phosphothreonyl residues fulfilling definite structural requirements.
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D007700:Kinetics; D009842:Oligopeptides / Q000378:metabolism; D010748:Phosphopeptides / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010765:Phosphorylase Phosphatase / Q000378:metabolism; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D054645:Protein Phosphatase 1; D051381:Rats
chemical_list: D009842:Oligopeptides; D010748:Phosphopeptides; D010769:Phosphothreonine; D000242:Cyclic AMP; D011494:Protein Kinases; C035158:protein phosphatase-T; D000469:Alkaline Phosphatase; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D010765:Phosphorylase Phosphatase; D000135:Acid Phosphatase