. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Consequences of administration of indoleacetic acid known to give rise to H2O2 upon reoxidation by molecular oxygen, we have inferred that the oxygen known to be required for the oxidation of lAA by the oxidase is involved in such a reaction. (c) The enzymatic activity is inhibited by cyanide, azide, and other heavy- metal inhibitors (Tang and Bonner, 1947; Wagenknecht and Burris, 1950). This fact, together wit
. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Consequences of administration of indoleacetic acid known to give rise to H2O2 upon reoxidation by molecular oxygen, we have inferred that the oxygen known to be required for the oxidation of lAA by the oxidase is involved in such a reaction. (c) The enzymatic activity is inhibited by cyanide, azide, and other heavy- metal inhibitors (Tang and Bonner, 1947; Wagenknecht and Burris, 1950). This fact, together with the apparent requirement for H2O2, led us to con- jecture that the oxidase was in fact composed of two moieties, a peroxide- generating system (presumably flavo-protein) and a peroxidase (Galston, Bonner, and Baker, 1953). This conjecture has been supported by the construction of an analogous system consisting of xanthine oxidase and horseradish root peroxidase, which will oxidize lAA when some substrate for the flavo-protein moiety is aor- Figure 6. The inhibition of lAA- oxidase activity by crystalline catalase. At each arrow, the reaction mixture was divided, and catalase added to one aliquot. I I so '^0 20- Cafalase. Catalase Catalase 80 100 120 ifO min supplied to the system (Galston et al., 1953). Since, in the lAA oxidase, no such additional substrate is required, we have further postulated that lAA, like dioxymaleic acid (Swedin and Theorell, 1940), is capable of giving rise to a peroxide used in its own peroxidation. This conjectured peroxigenic action of lAA was first directly demonstrated by Andreae and Andreae (1953) and later confirmed in our own laboratory (Siegel and Galston, 1955; Pilet and Galston, 1955). (d) One final fact concerning the enzyme needs to be recorded here, though its full significance is not yet completely appreciated. The action of the oxidase is greatly enhanced by certain cofactors, among which 2:4- dichlorophenol (DCP) (Goldacre, Galston,
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