Polyphenol oxidases (PPOs) are ubiquitous type-3 copper enzymes that catalyze the oxygen-dependent conversion of o-diphenols to the corresponding quinones. In most plants, PPOs are present as multiple isoenzymes that probably serve distinct functions, although the precise relationship between sequence, structure and function has not been addressed in detail. We therefore compared the characteri...

This paper describes the preparation of a biomimetic Langmuir-Blodgett film of tyrosinase incorporated in a lipidic layer and the use of lutetium bisphthalocyanine as an electron mediator for the voltammetric detection of phenol derivatives, which include one monophenol (vanillic acid), two diphenols (catechol and caffeic acid) and two triphenols (gallic acid and pyrogallol). The first redox pr...

Laccases (benzenediol:oxygen oxidoreductases, EC 1.10.3.2) catalyze the oxidation of a wide variety organic and inorganic substrates, typically p -diphenols with concomitant reduction oxygen (O 2 ) to water. Several molecules naturally occurring in foods beverages (e.g., phenols, carbohydrates, unsatured fatty acids thiol-containing proteins) can be modified by laccases. Hence, interaction betw...

Sponges (phylum Porifera), known to be the richest producers among the metazoans of bioactive secondary metabolites, are assumed to live in a symbiotic relationship with microorganisms, especially bacteria. Until now, the molecular basis of the mutual symbiosis, the exchange of metabolites for the benefit of the other partner, has not been understood. We show with the demosponge Suberites domun...

Mushroom tyrosinase, which is known to convert a variety of o-diphenols into o-benzoquinones, has been shown to catalyse an unusual oxidative decarboxylation of 3,4-dihydroxymandelic acid to 3,4-dihydroxybenzaldehyde [Sugumaran (1986) Biochemistry 25, 4489-4492]. The mechanism of this reaction was re-investigated. Although visible-region spectral studies of the reaction mixture containing 3,4-d...

BACKGROUND AND AIMS Polyphenol oxidases (PPOs) catalyse the oxidation of monophenols and/or o-diphenols to highly reactive o-quinones, which in turn interact with oxygen and proteins to form reactive oxygen species (ROS) and typical brown-pigmented complexes. Hence PPOs can affect local levels of oxygen and ROS. Although the currently known substrates are located in the vacuole, the enzyme is t...