title: Cobalt-dependent protein phosphatases from human cord blood erythrocytes. II. Further characterization of E2 casein phosphatase.
abstract: Of three casein phosphatases isolated from the cytosol of human cord blood erythrocytes two were cobalt-dependent, E2 and E3. In the presence of CoCl2, E2 activity was the most prominent. In addition to casein, E2 dephosphorylated phosvitin and p-nitrophenyl phosphate (p-NPP) with pH optima at 6.8-7.2 for proteins and 9.0 for p-NPP. The native enzyme had a molecular weight of 104,000 daltons after AcA-44 Ultrogel filtration. According to SDS/PAGE it consisted of two subunits, 78,000 and 15,000 daltons. The 104,000-dalton form exhibited Michaelis-Menten kinetics and had the greatest affinity for casein between protein substrates tested. Ethanol denaturated the enzyme by 80%. Optimal activation of E2 phosphatase was achieved with 5 mmol/l CoCl2 which did not affect the catalytic properties of the enzyme but did affect the rate of 'E-S' complex formation. Inorganic pyrophosphate was not inhibitory for the 104,000-dalton enzyme. Judging by all these properties the natural substrate for E2 casein phosphatase could be P-pyruvate kinase.
authors.affiliation: Institute of Biochemistry, Faculty of Medicine, Belgrade, Yugoslavia.
authors.forename: I
authors.initials: I
authors.lastname: Japundzić
authors.forename: E
authors.initials: E
authors.lastname: Levi
authors.forename: M
authors.initials: M
authors.lastname: Japundzić
mesh_terms: D002364:Caseins / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology*; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D004912:Erythrocytes / Q000201:enzymology*; D000431:Ethanol / Q000494:pharmacology; D005312:Fetal Blood / Q000201:enzymology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008970:Molecular Weight; D009596:Nitrophenols / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000097:blood*; D010774:Phosvitin / Q000378:metabolism; D011489:Protein Denaturation; D013379:Substrate Specificity
chemical_list: D002364:Caseins; D009596:Nitrophenols; D009943:Organophosphorus Compounds; C008644:nitrophenylphosphate; D003035:Cobalt; D000431:Ethanol; D010774:Phosvitin; D010749:Phosphoprotein Phosphatases