Native cytosolic protein phosphatase-1 (PP-1S) containing modulator (inhibitor-2) is an active enzyme.
In vitro, the modulator protein (inhibitor-2) slowly converts the catalytic subunit of protein phosphatase-1 (PP-1C) into an inactive 'MgATP-dependent form' that can be reactivated by the transient phosphorylation of modulator with GSK-3/FA. We report here that this modulator-induced inactivation of PP-1C can be blocked by addition (at pH 7.5) of either 0.3 mM NaF or 150 mM NaCl, or by raising the pH to 8.5. Making use of a combination of the latter conditions, we have partially purified a soluble modulator-associated form of PP-1 (PP-1S) from rabbit skeletal muscle as a spontaneously active enzyme that cannot be further activated by kinase GSK-3/FA. These observations argue against a role for the 'MgATP-dependent' form of PP-1S as an inactive reservoir of PP-1C. PP-1S was separated on aminohexyl Sepharose from another active, cytosolic species of PP-1, which appears to be a proteolytic product of the glycogen-bound PP-1G.
Bollen
M
M
Afdeling Biochemie, Fakulteit Geneeskunde, Katholieke Universiteit Leuven, Belgium.
DePaoli-Roach
A A
AA
Stalmans
W
W
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D054736:Elongation Factor 2 Kinase; D004789:Enzyme Activation / Q000187:drug effects; D004793:Enzyme Reactivators / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D009132:Muscles / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D011817:Rabbits; D012965:Sodium Chloride / Q000494:pharmacology; D012969:Sodium Fluoride / Q000494:pharmacology
D004793:Enzyme Reactivators; D012965:Sodium Chloride; D000255:Adenosine Triphosphate; D012969:Sodium Fluoride; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D054736:Elongation Factor 2 Kinase; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1