Abstract
Tyrosinase is responsible for the enzymatic browning of fruits and vegetables and usually catalyze the conversion of monophenols to o-diphenols and oxidation of diphenols to corresponding quinines. However, when 3,4-dihydroxymandelic acid is provided as the substrate, it catalyzes the oxidative decarboxylation reaction to generate 3,4-dihydroxybenzaldehyde (protocatechualdehyde, PA. In the present study, tyrosinase was purified from potato with 27.9 purification fold by salting out with ammonium sulfate, DEAE-Sepharose and Sephadex G-150 column chromatography. The purified tyrosinase was confirmed by tyrosinase active staining following SDS-PAGE. Tyrosinase activity was visualized in the gel as a dark band. The molecular weight of tyrosinase from potato was 38kDa as determined by SDS-PAGE. Purified tyrosinase mediated oxidative decarboxylation of 3,4-dihydroxymandelate. The identity of the reaction product, PA was confirmed by high-performance liquid chromatography (HPLC) as well as ultraviolet spectral studies. Phenol oxidase inhibitors such as potassium cyanide, sodium azide, and phenylthiourea inhibited the participation of the active site copper of the enzyme in the catalysis.
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