Studies on the destruction of indole-3-acetic acid by a species of Arthrobacter II. Properties of the oxidation system

Abstract

Some properties of the IAA-oxidizing activity of lyophilized cells of Artkrobacter sp. were examined. 1. IAA oxidation seems not to be catalysed by peroxidase, polyphenol oxidase, laccase or dehydrogenase, but by an oxidase system different from the one reported earlier. 2. The optimal pH for the oxidizing system is ca. 6.0, and the system is comparatively stable at pH 5 to 10. 3. The optimal substrate (IAA) level is 10−3 M. 4. Activity is inhibited by metal-chelating reagents, such as sodium azide, potassium cyanide, sodium diethyldithiocarbamate, potassium xanthogenate and 8-hydroxyquinoline, and sulfhydryl reagents, such as iodoacetamide, monofluoroacetic acid, p-chloromercuribenzoate, isatin, β-naphthoquinone and β-naphthoquinone-4-sulfonate. Hydroxybenzoic acid, sulfosalicylic acid and 2,4-dichlorophenol are also inhibitory. 5. None of the IAA analogs tested (indole, skatole, 2,3-dihydroxyindole, indole-3-aldehyde, -3-carboxylic acid, -3-propionic acid, -3-lactic acid, -3-butyric acid, 5-hydroxyindole-3-acetic acid and D, L-tryptophan) are oxidized by the cells, and some analogs (indole-3-carboxylic acid, -3-propionic acid, -3-butyric acid, 5-hydroxyindole-3-acetic acid, naphthalene-acetic acid and 2,4-D) are inhibitory at comparatively high concentrations. 6. The oxidizing activity is not stimulated by Mn++ and is inhibited by Co++, Cu++ and Hg++. 7. The oxidizing activity disappears completely within 6 hr at 30°, but is kept unchanged at least for two weeks at –20°.