ACTIVATION OF THE ATP.MG-DEPENDENT TYPE-1 PROTEIN PHOSPHATASE BY THE FE2+ ASCORBATE SYSTEM/

The ATP.Mg-dependent type 1 protein phosphatase is inactive as isolate d but can be activated in several different ways. In this report, we s how that the phosphatase can also be activated by the Fe2+/ascorbate s ystem. Activation of the phosphatase requires both Fe2+ ion and ascorb ate and the level of activation is dependent on the concentrations of Fe2+ ion and ascorbate. In the presence of 20 mM ascorbate, the Fe2+ i on concentrations required for half-maximal and maximal activation are about 0.3 and 3 mM, respectively. Several common divalent metal ions, including Co2+, Ni2+, Cu2+, Mg2+, and Ca2+ ions, canno cooperate with ascorbate to activate the phosphatase, and SH-containing reducing age nts such as 2-mercaptoethanol and dithiothreitol cannot cooperate with Fe2+ ion to activate the phosphatase, indicating that activation of t he phosphatase by the Fe2+/ascorbate system is a specific process. Mor eover, H2O2, a strong oxidizer, could significantly diminish the phosp hatase activation by the Fe2+/ascorbate system, suggesting that reduct ion mechanism other than SH-SS interchange is a prerequisite for the F e2+/ascorbate-mediated phosphatase activation. Taken together, the pre sent study provides initial evidence for a new mode of type 1 protein phosphatase activation mechanism.