Inhibition of polyphenol oxidase by copper-metallothionein from Aspergillus niger

Metallothionein from Aspergillus niger was found to be an inhibitor, in a model system, for the enzymic activity of a commercially purified mushroom tyrosinase. The inhibitory effect of metallothionein was higher on catechin oxidation compared with that on chlorogenic acid. The degree of inhibition of enzymic colour formation by metallothionein, using catechin as substrate; was lower than that of oxygen uptake; however, a reverse pattern was observed with chlorogenic acid as substrate. The demetallization of metallothionein did not increase its inhibitory effect on polyphenol oxidase whereas pre-incubation of the enzyme and metallothionein increased this inhibitory effect.