title: Activation of bovine heart ATP-MG2+-dependent phosphoprotein phosphatase: isolation of a phosphoenzyme intermediate and its conversion to the active form via a Mg2+-dependent autodephosphorylation reaction.
abstract: The ATP-Mg2+-dependent protein phosphatase, a holoenzyme form of type I protein phosphatase (phosphatase-1) requires the action of phosphatase-1 kinase (FA) for activation. The enzyme (75 kDa) purified from bovine heart consists of a catalytic (C) and a regulatory (R) subunit of 40 kDa and 34 kDa, respectively, and activation is associated with phosphorylation of the R-sub-unit. A procedure has been developed for isolation of [32P]phosphatase-1 ( [32P]E-P) in non-denatured form. In the absence of divalent cation, [32P]E-P is catalytically inactive and the phosphorylation is stable. Addition of Mg2+ triggers autodephosphorylation of [32P]E-P with concomitant generation of phosphorylase phosphatase activity. The autodephosphorylation/activation process is dependent on Mg2+ concentration. The KA value for Mg2+ is 0.6 mM. The phosphorylase phosphatase activity generated from the release of 1 mol. 32P is 1.1 X 10(12) units which is equivalent to 15,000 units per mg enzyme protein. The present findings provide direct evidence that the phosphorylated phosphatase-1 is not the active form (Ea). Instead, Ea is directly produced from the intermediate by a Mg2+-dependent autodephosphorylation reaction.
authors.forename: D J
authors.initials: DJ
authors.lastname: Price
authors.forename: H C
authors.initials: HC
authors.lastname: Li
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D009206:Myocardium / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1
chemical_list: D000255:Adenosine Triphosphate; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D008274:Magnesium