The polyphenol oxidase from
Chaetomium thermophile Isolate O-453 was examined for its substrate specificity. The purified enzyme acted on polyphenols but not on monophenols. Among the polyphenols and phenol-like compounds tested, those oxidized were
d-catechin (relative activity, 100%),
l-epicatechin (95.3%), chlorogenic acid (80.0%), pyrocatechol (53.8%), DOPamine (47.8%), guaiacol (87.5%), and N, N-dimethyl-
p-phenylenediamine (75.3%). Esculine (7.8%), resorcinol (0%),
p-quinone (0%),
o-phenylenediamine (1.3%), phenol (0%), and L-tyrosine (0%) were
scarcely oxidized. The purified enzyme was inhibited by potassium xanthogenate, thiourea, cysteine, potassium cyanide, and sodium azide. Mercuric and ferrous ions inactivated the enzyme. Carbon monooxide did not inhibit the activity (residual activity, 92.0%). SDS-polyacrylamide gel electrophoresis showed that the purified enzyme (mw, 98, 000) is a trimer composed of three of the same kinds of monomers (mw, 36, 000). These data indicate that the polyphenol oxidase from
C. thermophile Isolate O-453 is a copper-containing protein and is classified as laccase [benzenediol: oxygen oxidoreductase, EC 1.10.3.2].
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