Assay of B16F10 intracellular tyrosinase activity
Cellular tyrosinase activity was determined as described
previously [34] with slight modifications. Briefly, the cells
were treated with α-MSH (100 nM) for 24 h, and then
intracellular tyrosinase activity was measured after treatment
with various concentrations of M. grandiflora L.
flower extract (final concentration 10, 15, 20%; v/v) or
arbutin (2.0 mM) for 24 h. After these treatments, the
cells were washed twice with phosphate-buffered saline
and homogenized with 50 mM PBS (pH 7.5) buffer containing
1.0 % Triton X-100 and 0.1 mM PMSF. Intracellular
tyrosinase activity was monitored as follows: Cell
extracts (100 μL) were mixed with freshly prepared
L-DOPA solution (0.1% in phosphate-buffered saline)
and incubated at 37°C. The absorbance at 490 nm was
measured with microplate reader Gen 5TM (BIO-TEK Instrument,
Bermont, USA) to monitor the production of
dopachrome, corrected for auto-oxidation of L-DOPA.