Conversion of active protein phosphatase to the ATP‐Mg‐dependent enzyme form by inhibitor‐2

Abstract

Brandt et al. [ 1, The regulatory role of these heat-stable proteins in the control of phosphatase activity was accentuated when two heat-stable inhibitors, termed inhibitor-l and -2 were discovered and the inhibitory capacity of inhibitor-l demonstrated to depend upon its phosphorylation by the cyclic AMP-dependent protein kinase Heat-stable phosphatase inhibitors have since been identified in a variety of animals and tissues [S-l 0] and purified to homogeneity from rabbit muscle (inhibitor-l , -2) [8 ,101 and rabbit liver [7]. The implication of inhibitor-l in the hormonal regulation of glycogen metabolism has been clearly demonstrated [ll-131. We have reported the purification and characterisation of an ATP-Mgdependent protein phosphatase system from rabbit muscle [14-191: an inactive multifunctional protein phosphatase (FC) was shown to be activated by another protein factor (FA) in the presence of ATP-Mg ions (without phosphorylation). This report provides evidence that purified inhibitor-2 preparations [lo] have the capacity to reverse the F, and ATP-Mg-mediated activation.