Native cytosolic protein phosphatase‐1 (PP‐1S) containing modulator (inhibitor‐2) is an active enzyme

[摘要]

In vitro, the modulator protein (inhibitor-2) slowly converts the catalytic subunit of protein phosphatase-1 (PP-1_c) into an inactive ‘MgATP-dependent form’ that can be reactivated by the transient phosphorylation of modulator with GSK-3/F_A. We report here that this modulator-induced inactivation of PP-1_C 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/F_A. These observations argue against a role for the ‘MgATP-dependent’ form of PP-1S as an inactive reservoir of PP-1_C. 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.

[学科分类] 生物化学/生物物理

[关键词] Protein phosphatase;Inhibitor-2;Chaperone;Skeletal muscle;GSK-3/FA;glycogen synthase kinase-3;also termed protein kinase FA;PP-1;protein phosphatase-1;PP-1S;soluble (cytosolic) PP-1;PP-1G;glycogen-bound protein phosphatase-1;PP-1C;catalytic subunit of protein phosphatase-1