removed and to each well was added 100 u03bcl culture medium containing different concentration of medicine to be screened and for blank control group only culture medium was added each group was in quadruplicate and the culture medium was renewed every other day after being incubated for 6 days each well was washed by pbs without ca 2 and mg 2 and then 100 u03bcl triton x solution 0 5 was added to each well after being vibrated in ultrasound for 30 minutes 50 u03bcl l dopa solution 10 mm l was added to each well and the samples was kept at 37 u00b0 c for 3 hours the absorbance of each well was measured at a wavelength of 490 nm reference wavelength 620 nm by enzyme label instrument influence rate of the activity of tyrosinase average absorbance of the group of medicine to be screened average absorbance of control group 100 according to the results of mtt experiment b16f10 cells were seeded in the 6 well plate respectively at a density of 2 10 4 well and incubated under 5 co 2 and at 37 u00b0 c for 24 h then the supernatant was removed and to each well was added 6 0 ml culture medium.