Figure 4.
Activity of Arabidopsis SphK toward Sph in mixed micelles with Triton X-100 according to the surface binding model. A, SphK activity in leaf lysates was measured as a function of the sum of the molar concentrations of Triton X-100 (TX) plus Sph at set mole fractions (MF) of Sph. Data are means ± se of five independent experiments. V refers to picomoles of Sph hydrolyzed per minute per milligram of enzyme. B, Reciprocal plot of the data in A. C, Replot of 1/V intercepts obtained in B versus the reciprocal of the mole fraction of Sph; R2 = 0.9896. D, Replot of slopes obtained in B versus the reciprocal of the mole fraction of Sph; R2 = 0.9210. The lines drawn in A and B were a result of a least-squares analysis of the individual data sets using Equation 2. They are statistically different [P(F4,21 > 36.75) < 0.00001].