(p,p′n), (p,p′γ

The MgATP-Dependent Protein Phosphatase and Protein Phosphatase 1 Have Identical Substrate Specificities

“…When protein phosphatase 1 and the MgATP-dependent protein phosphatase were diluted to give the same phosphorylase phosphatase activity, very similar amounts of inhibitor 1 and inhibitor 2 were required to produce 50 inhibition. The phosphorylase kinase phosphatase and glycogen synthase phosphatase activities of the MgATP-dependent protein phosphatase were inhibited in a similar manner to the phosphorylase phosphatase activity (results not illustrated), as has been reported previously for protein phosphatase 1 [15,27,40].…”

“…Protein phosphatase 1 dephosphorylates the [hubunit of phosphorylase kinase much faster than the a-subunit, whereas protein phosphatase 2 dephosphorylates the a-subunit much Faster than, the fl-subunit [9,41]. Protein phosphatase 1 is inhibited by nanomolar concentrations of two proteins termed inhibitor 1 and inhibitor 2 which have no effect on the activity of protein phosphatase 2 [9,15,21,27,40].…”

“…a) It accounted for 80-90% of the phosphorylase phosphatase and glycogen synthase phosphatase activity that could be measured in muscle extracts under optimal conditions, whereas protein phosphatase 2 accounted for only 5 -10 x of the phosphorylase phosphatase and 10-15 x of the glycogen synthase phosphatase activity [26,27]. b) Protein phosphatase 1 accounted for > 95 "/, of the activity towards the P-subunit of phosphorylase kinase [26,27,411. Since the activity of phosphorylase kinase is determined by the state of phosphorylation of the P-subunit [ I l , 281, protein phosphatase 1 was the only significant protein phosphatase activity that could inactivate phosphorylase kinase.…”

“…Plzosphorylose Kinuse a. The incubation (10 mi) was carried out at 20 'C and comprised phosphorylase kinase h (2.0 mg/ml), the catalytic subunit of cyclic-AMP-dependent protein kinase (0.3 Ujml-see [27] for definitions of units), 10 mM sodium glycerophosphate pH 7.0, 0.4 mM EDTA, 0.1 "', (v/v) 2-mercaptoethanol, 0.2 mM EGTA, 2.0 mM magnesium acetate and 0.2 mM [y-"PIATP. The reaction was initiated with MgATP, and terminated when the amount of phosphate in the x-subunit had reached the level of the fl-subunit (determined by a prior pilot phosphorylation), by addition of 0.1 vol.…”

“…Protein phosphatase 1 is inhibited by nanomolar concencentration of the two muscle proteins termed inhibitor 1 and inhibitor 2 [15,40]. These proteins do not inhibit type-2 protein phosphatases [40,42] or a specific histone phosphatase [27]. Similarly, the MgATP-dependent protein phosphatase has been shown to be inhibited by two heat-stable liver proteins which appear to be analogous to inhibitor 1 and inhibitor 2 from muscle [43].…”