Figure 2.

PI-PLC–mediated hydrolysis of [³H]PI in liposomes. A, liposomes composed of egg PC, egg PA (9:1, molar ratio), and trace amounts of [³H]PI were treated with different amounts of PI-PLC at room temperature. At the indicated times, aliquots of the suspensions were removed, and lipids were extracted using a two-phase extraction system. Radioactivity in the upper aqueous and lower organic phases, containing 1,2-cyclic [³H]inositol phosphate/[³H]inositol 1-phosphate and ([³H]PI), respectively, was used to calculate the fraction of [³H]PI hydrolyzed by PI-PLC. The data points are from three independent experiments done in the presence of 0.5 μl (filled circles), 1.0 μl (open squares), or 3.0 μl (filled triangles) PI-PLC. In control incubations in the absence of PI-PLC, [³H]PI hydrolysis was <3%. For better visibility, the inset shows the curves during the first 2 min of incubation. The data were fitted to a one-phase exponential function. B, half-times of [³H]PI hydrolysis in the presence of different amounts of PI-PLC calculated from the curves shown in A. The data are mean values ± standard deviations from three independent experiments.