Characterization of a tyrosinase from Amanita muscaria involved in betalain biosynthesis

A tyrosinase was characterized from the betalain-containing pileus of the mushroom Amanita muscaria. The enzyme was located exclusively in the coloured parts of the mushroom and hydroxylated tyrosine to 3:(3,4-dihydroxyphenyl)-alanine (DOPA), suggesting that it is involved in betalain biosynthesis. The tyrosinase was not specific for tyrosine, and in addition to the monophenolase activity, the enzyme also oxidized diphenols to o-quinones (diphenolase activity). The native enzyme appeared to be a heterodimer of two subunits with M(r)s of 27 000 and 30 000, which is unusual for tyrosinases. Typical tyrosinase inhibitors such as tropolone, 2-mercaptobenzothiazole and benzoic acid strongly inhibited the enzyme.