Abstract
The ATP.Mg-dependent type 1 protein phosphatase is inactive as isolated but can be activated in several different ways. In this report, we show that the phosphatase can also be activated by the Fe2+/ascorbate system. Activation of the phosphatase requires both Fe 2+ ion and ascorbate and the level of activation is dependent on the concentrations of Fe 2+ ion and ascorbate. In the presence of 20 mM ascorbate, the Fe 2+ ion concentrations required for half-maximal and maximal activation are about 0.3 and 3mM, respectively. Several common divalent metal ions, including Co 2+ , Ni 2+ , Cu 2+ , Mg 2+ , and Ca 2+ ions, cannot cooperate with ascorbate to activate the phosphatase, and SH-containing reducing agents such as 2-mercaptoethanol and dithiothreitol cannot cooperate with Fe 2+ ion to activate the phosphatase, indicating that activation of the phosphatase by the Fe2+/ascorbate system is a specific process. Moreover, H 22 O 2 , a strong oxidizer, could significantly diminish the phosphatase activation by the Fe 2+ /ascorbate system, suggesting that reduction mechanism other than SH-SS interchange is a prerequisite for the Fe 2+ /ascorbate-mediated phosphatase activation. Taken together, the present study provides initial evidence for a new mode of type 1 protein phosphatase activation mechanism.