FIG. 3.

Cation specificity of p110α, PI3K-C2α, and PI3K-C2β and their sensitivity to inhibition by wortmannin. (A and B) Recombinant p85α-p110α, PI3K-C2α, and PI3K-C2β were assayed for lipid kinase activity using either PtdIns (A) or PtdIns(4)P (B) in the absence (−) or presence of either Ca²⁺, Mg²⁺, or Mn²⁺. Reaction products were extracted, fractionated by TLC, and examined by autoradiography. (C) p85α-p110α, PI3K-C2α, and PI3K-C2β were also examined for their ability to phosphorylate PtdIns in the presence of either Ca²⁺ or Mg²⁺ as the divalent cation and in the absence (−) or presence (+) of wortmannin (50 nM).