Figure 7. Reactivation of mammalian PP2Ai by yeast as well as mammalian PTPA.

Purified PP2Ai (1 nM) was incubated with the indicated concentrations of purified recombinant mammalian PTPA (◆), Ypa1 (■) and Ypa2 (▲) with ATP, Mg²⁺ and assayed for (A) basal and (B) protamine-stimulated phosphorylase a phosphatase activity. (C) GST pull-down assay of IVTT [³⁵S]methionine-labelled human PP2A_Cα. (D) Ypa2 inhibits Ypa1 activity. Mammalian PP2Ai is reactivated by 125 pM Ypa1 as in (A, B) in the presence of the indicated concentrations of Ypa2. Subsequently, basal and protamine-stimulated phosphorylase a phosphatase activity was measured.