G beta gamma-Copurified Lipid Kinase Impurity from Sf9 Cells

G-protein beta gamma dimers are prime regulators transmitting extracellular signals to wide-ranging cellular effectors including phosphoinositide 3-kinase (PI3K) isoforms beta and gamma. Recombinant G beta gamma purified from Sf9 cells via metal-affinity and anion exchange chromatography exhibited a wortmannin-insensitive phospholipid kinase activity that copurified from the insect cells. To exclude false-positive results of G beta gamma-dependent lipid kinase activity, the elimination of insect phospholipid kinase from G beta gamma protein samples is necessary to avoid interference with the intrinsic lipid kinase activity of PI3K isoforms in reconstitution experiments. Here we describe an improved procedure of G beta(1)gamma(2) purification from cell membranes that separates the contaminating phospholipid kinase.