title: Identification of pseudo 'phosphothreonyl-specific' protein phosphatase T with a fraction of polycation-stimulated protein phosphatase 2A.
abstract: Protein phosphatase T from rat liver, so termed due to its activity toward [32P-Thr]casein and its marked preference for the phosphopeptide Arg-Arg-Ala-Thr(P)-Val-Ala over its phosphoseryl derivative (Donella Deana, A., Marchiori, F., Meggio, F. and Pinna, L.A. (1982) J. Biol. Chem. 257, 8565-8568), is shown here to belong to the family of type 2A protein phosphatase according to Cohen's nomenclature (Ingebritsen, T.S. and Cohen, P. (1983) Eur. J. Biochem. 132, 255-261). In particular, protein phosphatase T is endowed with phosphorylase phosphatase activity that is stimulated by protamine, histone H1 and heparin, it is inhibited by spermine, it does not bind to heparin-Sepharose and it readily dephosphorylates the phosphopeptide Arg-Arg-Leu-Ser(P)-Ile-Ser-Thr-Glu-Ser reproducing the phosphorylation site of the alpha-subunit of phosphorylase kinase. The Mr of protein phosphatase T determined by gel filtration under non-denaturating conditions is about 150 kDa and its activity ratio toward histone H1 phosphorylated by protein kinase C versus histone H1 phosphorylated by cAMP-dependent protein kinase is unusually high. Some properties of protein phosphatase T, such as its weak binding to DEAE-cellulose and its high stimulation by protamine as compared to a relatively poor stimulation by histone H1, suggest that it may be similar to subtype 2Ao of protein phosphatase 2A.
authors.affiliation: Istituto di Chimica Biologica dell'Università di Padova, Italy.
authors.forename: A D
authors.initials: AD
authors.lastname: Deana
authors.forename: L A
authors.initials: LA
authors.lastname: Pinna
mesh_terms: D000818:Animals; D003636:DEAE-Cellulose / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology; D006657:Histones / Q000378:metabolism / Q000494:pharmacology; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000145:classification* / Q000302:isolation & purification* / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism*; D011479:Protamines / Q000494:pharmacology; D054648:Protein Phosphatase 2; D051381:Rats; D011919:Rats, Inbred Strains; D013096:Spermine / Q000494:pharmacology; D013379:Substrate Specificity; D013912:Threonine / Q000031:analogs & derivatives*
chemical_list: D006657:Histones; D011479:Protamines; D010769:Phosphothreonine; D013096:Spermine; D013912:Threonine; D006493:Heparin; D003636:DEAE-Cellulose; C035158:protein phosphatase-T; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2