Figure 6.
Distribution of SphK activity in Arabidopsis leaves. A and B, SphK activity was measured in cytosolic (A) and membrane (B) fractions from leaves with the indicated concentrations of Sph added as a BSA complex. Data were fitted to the Michaelis-Menten equation as described in “Materials and Methods”; R2 = 0.7189 and 0.9902 for A and B, respectively. C and D, Phosphorylation of various long-chain bases (50 μm) added either as a BSA complex or as Triton X-100 mixed micelles was measured in cytosolic (C) and membrane (D) fractions from leaves. Data are means ± se of three independent experiments. Note change in scale between A and C, and B and D. When error bars are not indicated, the se is less than the size of the symbols.