title: Purification and characterization of three distinct types of protein phosphatase catalytic subunits in bovine platelets.
abstract: The catalytic subunits of bovine platelet protein phosphatases were separated into three distinct forms by chromatography on heparin-Sepharose. Each phosphatase was further purified to apparent homogeneity as judged in sodium dodecyl sulfate-polyacrylamide gel yielding single protein bands of 37, 41, and 36 kDa. The 37-kDa phosphatase was excluded from heparin-Sepharose and preferentially dephosphorylated the alpha-subunit of phosphorylase kinase. It was stimulated by polycations (polybrene or histone H1) and was inhibited by okadaic acid (IC50 = 0.3 nM), but its activity was not influenced by inhibitor-2 or heparin. The 41-kDa phosphatase was eluted from heparin-Sepharose by 0.20-0.25 M NaCl and preferentially dephosphorylated the beta-subunit of phosphorylase kinase. It was stimulated by polycations and inhibited by okadaic acid (IC50 = 2 nM), but its activity was not affected by inhibitor-2 or heparin. The 36-kDa phosphatase was eluted from heparin-Sepharose by 0.45-0.50 M NaCl and preferentially dephosphorylated the beta-subunit of phosphorylase kinase. It was inhibited by inhibitor-2, heparin, histone H1, and okadaic acid (IC50 = 70 nM). The 37- and 36-kDa phosphatases can be classified as type-2A and type-1 enzymes, respectively. The 41-kDa phosphatase does not precisely fit the criteria of either type, showing only partial similarities to both type-1 and type-2A enzymes and it may represent a novel type of protein phosphatase in bovine platelets.
authors.affiliation: Department of Medical Chemistry, University Medical School of Debrecen, Hungary.
authors.forename: F
authors.initials: F
authors.lastname: Erdödi
authors.forename: C
authors.initials: C
authors.lastname: Csortos
authors.forename: L
authors.initials: L
authors.lastname: Sparks
authors.forename: A
authors.initials: A
authors.lastname: Murányi
authors.forename: P
authors.initials: P
authors.lastname: Gergely
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000201:enzymology*; D002417:Cattle; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D004988:Ethers, Cyclic / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000097:blood* / Q000302:isolation & purification; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology
chemical_list: D004988:Ethers, Cyclic; D046911:Macromolecular Substances; D010975:Platelet Aggregation Inhibitors; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases