Abstract
A major tyrosinase isoform was isolated from the cap skins of Portabella mushrooms after chromatography on DEAE cellulose and hydroxylapatite columns. The isolated enzyme had a pI of 4.3 and a subunit molecular weight of 48 kDa while the native size was estimated to be 43 kDa. Western blotting indicated that 48 and 26 kDa cross-reacting proteins were present in the isolated fraction. This tyrosinase isoform had a pH optimum of 7.0 and was most active with catechol, tert-butylcatechol, andpyrogallol as substrates. The enzyme was severely inhibited by erythorbic acid, glutathione, cysteine, tropolone, salicylhydroxamic acid, kcjic acid, and diethyldithiocarbamic acid, but little inhibition was observed using honey extracts, borax, resveratrol, cyclodextrins, or a copper chelating peptide.
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