FIGURE 4.

Dependence on a cyl-CoA chain length of inhibition of CerS activity by FTY720. A, CerS activity was assayed in homogenates (100 μg of protein) of HEK cells using 0.25 μCi of [4,5-³H]sphinganine/15 μm sphinganine, 20 μm defatted BSA and 50 μm of either C18- (for CerS1) or C16-acyl-CoA (for CerS5). B, CerS4 activity was assayed in homogenates (100 μg of protein) from CerS4-overexpressing cells using 0.25 μCi of [4,5-³H]sphinganine, 15 μm sphinganine, 20 μm defatted BSA, and 50 μm of either C18- or C20-acyl-CoA. The specific activity of CerS4 in the absence of FTY720 toward C18-CoA was 444 pmol of ceramide formed per min per mg of protein and 389 pmol of ceramide formed per min per mg of protein toward C20-CoA in a typical experiment. The results are the means ± S.D. of two independent experiments, each of which was repeated at least three times with similar results.