Fig. 2. Effects of S1P and kojic acid on melanogenesis in Mel-Ab cells. Cells were cultured with 1-10 µM S1P or 1-100 µM kojic acid for 5 days, and the tyrosinase activity (A) or melanin content (B,C) was measured, as described in Materials and Methods. (D) To test the direct effect on tyrosinase, tyrosinase activity was measured in a cell-free system, also as described in Materials and Methods. Results are the average of three independent experiments ± s.d. **P<0.01, *P<0.05 compared with control.