title: Platelet protein phosphatases and their endogenous substrates.
abstract: One p-nitrophenyl phosphate phosphatase (A) and five protein phosphatases (B, C, D, E, F) with neutral pH optimum (7.0-7.5) were partially purified from human platelets. Protein phosphatases were activated by Mn2+ (B-F), Mg2+ (D, F) or Ca2+ (F) but all of them had substantial activity even in the presence of EDTA. The activity of phosphatase D was predominant when assayed in the presence of EDTA. Phosphatase F was significantly enhanced by Ca2+ and calmodulin and therefore considered to be calcineurin. Without strict substrate specificity, all protein phosphatases (B-F) dephosphorylated phosphoproteins like actin binding protein, 47k protein and myosin light chain. Thus, it was suggested that protein phosphatases might play a role in the down regulation of platelet function not only in the resting but agonist-stimulated platelets.
authors.affiliation: Second Department of Surgery, Osaka University Medical School, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Sakon
authors.forename: J
authors.initials: J
authors.lastname: Kambayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Kajiwara
authors.forename: Y
authors.initials: Y
authors.lastname: Uemura
authors.forename: E
authors.initials: E
authors.lastname: Shiba
authors.forename: T
authors.initials: T
authors.lastname: Kawasaki
authors.forename: T
authors.initials: T
authors.lastname: Mori
mesh_terms: D001792:Blood Platelets / Q000201:enzymology*; D002118:Calcium / Q000494:pharmacology; D002848:Chromatography, DEAE-Cellulose; D004492:Edetic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D006657:Histones / Q000378:metabolism; D006801:Humans; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D009596:Nitrophenols / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000097:blood* / Q000302:isolation & purification; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D013379:Substrate Specificity; D013917:Thrombin / Q000494:pharmacology
chemical_list: D006657:Histones; D009596:Nitrophenols; D009943:Organophosphorus Compounds; D010750:Phosphoproteins; C008644:nitrophenylphosphate; D008345:Manganese; D004492:Edetic Acid; D010749:Phosphoprotein Phosphatases; D013917:Thrombin; D008274:Magnesium; D002118:Calcium