Purification of tyrosinase by Fast Protein Liquid Chromatography
The supernatant was loaded onto a cation exchange column (SP-Sepharose FF, GE Healthcare, length = 10 cm, diameter = 2.6 cm) and equilibrated with 20 mM sodium acetate, pH 4.5. Bound proteins were eluted with a linear gradient of sodium chloride (0–1 M) at a flow rate of 5 mL/min (see Fig. 1A). All collected fractions were tested photometrically for monophenolase and diphenolase activity. Fractions containing activity were pooled, ultra filtrated (size exclusion membrane of 10 kDa) and centrifuged (4000 rpm, 4 °C) to remove sodium chloride. The protein solution was then applied to a MonoS HR 5/50 Gl column (cation exchange column, GE Healthcare, length = 50 mm, diameter = 5 mm) and eluted with a linear gradient of sodium chloride (0–0.7 M) at a flow rate of 1 mL/min. Two forms were eluted at a conductivity of 13 and 16 mS/cm (see Fig. 1B), respectively. Fractions containing the first and the second eluted protein form were separately pooled and again loaded on the MonoS HR 5/50 Gl column under same conditions for removing further non-target proteins in a final polishing step (see Fig. 1C/D).