Aromatic carboxylic acids strongly inhibited 4-methylcatechol oxidation by an o-diphenol oxidase extracted from sweet cherry fruits (Prunus uvium). Esterification of the acids decreased their inhibitory strength. Inhibitors containing the benzene nucleus showed a greater effectiveness than the corresponding aliphatic and heterocyclic compounds (except 2-naphthalenecarboxylic acid). Similar inhibitory effects were observed by replacing the benzene ring with a highly unsaturated open chain. The inhibitory properties of benzoic acid, cinnamic acid, p-coumaric acid and 3,4-dihydroxybenzoic acid were investigated. It is proposed that the catalytic and inhibitory sites are close together in the enzyme molecule.

S An enzymatic system capable of degrading cyanidin‐3‐glucoside in the absence of phenols is present in the skin of sweet cherries; contrarily, the pulp homogenate degraded the anthocyanin only in the presence of phenols. The degradation of this pigment as a function of pH was studied for two polyphenol oxidases isolated from the fruit pulp on DEAE‐cellulose with chlorogenic acid, D (+) catechine and pyrocatechol substrates. The decoloration was influenced by the anthocyanin structure at different pH and by the nature of the quinone obtained by enzymatic oxidation. The anhydrobase appeared to be the form of the anthocyanin most susceptible to oxidation. The degradation occurred according to the oxidation kinetics of the phenol substrate and was inhibited by ascorbic acid, indicating that the quinone's degradation of the anthocyanin occurred by a consecutive‐type mechanism.

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Aqueous solutions of ethylene glycol and hydroxylamine in a 10 : 1 weight ratio were irradiated with an immersion-type. mercury-vapour lamp, under static and dynamic conditions. The photochemical products obtained were fractionated by means of ion-exchange resins, gel filtration on Sephadex G 10, paper chromatography, and thin-layer chromato-Biuret reaction was carried out on the various fractions, and different nitrogen forms as well as amino acids, before and after hydrolysis, were determined. Irradiation was found to