JOURNAL OF COSMETIC SCIENCE 140 to identify a novel tyrosinase inhibitor, we decided to screen compounds combining the structural features known to participate in the interaction between tyrosinase and its substrates or inhibitors. This way, we have selected N-feruloyldopamine as the most potent substrate-mimicking inhibitor of tyrosinase. N-feruloyldopamine has been previously isolated from Atraphaxis spinosa (22) with poor yield. We used organic synthesis to obtain this molecule in suffi cient amounts to evaluate its melanogenesis inhibition abilities in vitro. Results show that N-feruloyldopamine exerted 45% inhibition when used at 30 μM in cultured NHEMs. Using linear regression, the IC50 of N-feruloyldopamine in this model was evaluated at 48.3μM (% inhibition = −0.8042 × [N-feruloyldopamine] + 90.698 R2 = 0.9068). Contrarily, N-feruloyldopamine did not exert any inhibitory effect toward Figure 3. Measurement of (A) human and (B) mushroom tyrosinase activities. Mean ± SD, n = 6. **, ***Statistically signifi cant vs. untreated control, p 0.01 and p 0.001, respectively.

INHIBITORY EFFECTS OF N-FERULOYLDOPAMINE 141 mushroom tyrosinase. Comparable results have previously been reported, notably with p-coumaric acid (23). Such a difference between the two models might be explained by the different structural features of human and mushroom tyrosinases. Although both ty- rosinases exhibit high homology in their active sites, human tyrosinase is a monomeric protein while mushroom tyrosinase is mostly tetrameric. Moreover, regulation of mush- room tyrosinase differs signifi cantly in several respects from mammalian tyrosinase, nota- bly with regard to post-translational modifi cations (4). It is also worth noting that qRT-PCR results showed no effect of N-feruloyldopamine on tyrosinase gene expression in normal human melanocytes (data not shown). Figure 4. Total melanin content of murine melanoma B16-F10 cells. Mean ± SD for n = 6. **Statistically signifi cant vs. untreated control, p 0.01. Figure 5. Radical-scavenging activity of N-feruloyldopamine. DPPH assay. Mean ± SD, n = 6. *,**Statisti- cally signifi cant vs. untreated control, p 0.05 and p 0.01, respectively.