Melanin content was determined by the method of Whittaker [12]. Cells were harvested with 0.5% trypsin and suspended in PBS for cell counting. The cell pellet was extracted with 5% trichloroacetic acid three times, with ether-alcohol
(1:3) twice and with absolute ether once. The air-dried residue was dissolved in 3 ml of 0.85 M KOH and was heated for 10 min at 100°C. Optical density of the solution at 400 nm was measured. Tyrosinase activity was assayed by the
modified method of Steinberg and Whittaker [13]. The cell pellet was disrupted in 0.5% sodium deoxycholate (DOC) for 30 min at 4°C. The reaction mixture containing the cell lysate and 0.04% L-3,4-dihydroxyphenyl-alanine (L-DOPA)
(Wako Pure Chemical Industries, Japan) in 0.1 M sodium phosphate buffer, pH 6.8 [14], was incubated for 10 min at 37°C. The change in optical density at 475 nm during the first few minutes was measured while it was in the linear phase. Correction for DOPA autoxidation was performed and specific activity was expressed as AOD at 475 nm/min per mg protein. Protein content was estimated by the method of Lowry et al. [15] with the standard protein solution of bovine serum albumin (BSA).