Catabolism of indole-3-acetic acid in citrus leaves: identification and characterization of indole-3-aldehyde oxidase

Abstract

1993. Catabolism of indole-3-aeetie aeid in citrus leaves: identification and eharaeterization of indole-3-aldehyde oxidase. -Physioi Plant. 89: 220-226.A new enzyme, named indole-3-aldehyde oxidase (IAldO). was identified in citrus (Citrus sinensis L. Osbeck cv. Shamouti) leaves. The enzyme was partially purified by (NH4)2SO4 fractionation. Sephadex G-200 gel filtration and DEAE-cellulose ion exehange ehromatography. IAldO catalyzes the oxidation of indole-3-aldehyde (IAId) to indole-3-carboxylic acid (ICA) with the production of H^O,. The enzyme is highly specific for IAId. The apparent K,^ of the enzyme for IAId is 19 [iM. The optimum oxidation of IAId occurs at pH 7.5. The molecular mass of the enzyme, as determined by Sepharose-6B gel filtration, is about 200 kDa. Based on inhibitor studies, it is concluded that IAldO is not a flavin-linked oxidase and there is no requirement for free sulfhydryl groups or divalent cations for maximum activity. The enzyme is strongly inhibited by benzaldehyde. Ethylene pretreatment. wounding and aging of leaf tissues did not affect enzyme aetivity. suggesting that the enzyme is constitutive in citrus tissues.

The biosynthesis of shikimate metabolites

“…The biosynthesis of anthranilamide phytoalexins, derivatives of N-benzoylanthranilate, in plants of the Cruciferae is included in a recent review. 'O 87) in the P-subunit enzyme has been deduced to play a critical role in its function, by forming an internal aldimine with pyridoxal 5'-pho~phate.~~ It also appears to be important for substrate and product release. The presence of L-and D-tryptophan aminotransferases has been reported in maize (Zea mays) c~leoptiles.~~ Two forms of the enzyme accepting the L-isomer were separated.…”

“…Also, in contrast to lignin biosynthesis, stereochemically-controlled couplings are operative which lead to enantiomerically pure products. The biosynthesis of (-)-matairesinol ( 90) is known to proceed from coniferyl alcohol (78) as shown in Scheme 26, probably via the diquinonemethide (86) with the first-formed isolable lignan being ( + )-pinoresinol (87). This furanofuran lignan is then ring-opened by reductive enzymes giving (-)secoisolariciresinol (89).…”