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Mechanism of indole-3-acetic acid oxidation by plant peroxidases: anaerobic stopped-flow spectrophotometric studies on horseradish and tobacco peroxidases.

ABSTRACT: Indole-3-acetic acid (IAA) is a powerful plant growth regulator. The oxidative decarboxylation of IAA by plant peroxidases is thought to be a major degradation reaction involved in controlling the in vivo level of IAA. Horseradish peroxidase isoenzyme C and an anionic tobacco peroxidase isolated from transgenic Nicotiana sylvestris have been used in experiments in vitro designed to determine the mechanism of IAA oxidation. In particular, the initial reduction of ferric to ferrous enzyme, a key step in previously proposed mechanisms, has been investigated by rapid-scan stopped-flow spectrophotometry under strictly anaerobic conditions and at defined oxygen concentrations. The data provide the first evidence for a ternary complex comprising peroxidase, IAA and oxygen that is kinetically competent both at the initiation stage and during the catalytic cycle of IAA oxidation. A general scheme describing the oxidative cycles of both anionic and cationic peroxidases is proposed that includes native ferric enzyme and compound II as kinetically competent intermediates. For anionic peroxidases, addition of hydrogen peroxide switches on the oxidative cycle thereby promoting IAA oxidation. 2-Methyl-IAA is not a substrate of the oxidase reaction, suggesting a specific interaction between plant peroxidases and IAA.

SUBMITTER: Gazaryan IG

PROVIDER: S-EPMC1216987 | biostudies-other | 1996 Feb

REPOSITORIES: biostudies-other

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Oxidation of indole-3-acetic acid by dioxygen catalysed by plant peroxidases: specificity for the enzyme structure.

Project description:Indole-3-acetic acid (IAA) can be oxidized via two mechanisms: a conventional hydrogen-peroxide-dependent pathway, and one that is hydrogen-peroxide-independent and requires oxygen. It has been shown here for the first time that only plant peroxidases are able to catalyse the reaction of IAA oxidation with molecular oxygen. Cytochrome c peroxidase (CcP), fungal peroxidases (manganese-dependent peroxidase, lignin peroxidase and Arthromyces ramosus peroxidase) and microperoxidase were essentially inactive towards IAA in the absence of added H2O2. An analysis of amino acid sequences allowed five structurally similar fragments to be identified in auxin-binding proteins and plant peroxidases. The corresponding fragments in CcP and fungal peroxidases showed no similarity with auxin-binding proteins. Five structurally similar fragments form a subdomain including the catalytic centre and two residues highly conserved among 'classical' plant peroxidases only, namely His-40 and Trp-117. The subdomain identified above with the two residues might be responsible for the oxidation of the physiological substrate of classical plant peroxidases, IAA.

| S-EPMC1220287 | biostudies-other

An updated view on horseradish peroxidases: recombinant production and biotechnological applications.

Project description:Horseradish peroxidase has been the subject of scientific research for centuries. It has been used exhaustively as reporter enzyme in diagnostics and histochemistry and still plays a major role in these applications. Numerous studies have been conducted on the role of horseradish peroxidase in the plant and its catalytic mechanism. However, little progress has been made in its recombinant production. Until now, commercial preparations of horseradish peroxidase are still isolated from plant roots. These preparations are commonly mixtures of various isoenzymes of which only a small fraction has been described so far. The composition of isoenzymes in these mixed isolates is subjected to uncontrollable environmental conditions. Nowadays, horseradish peroxidase regains interest due to its broad applicability in the fields of medicine, life sciences, and biotechnology in cancer therapy, biosensor systems, bioremediation, and biocatalysis. These medically and commercially relevant applications, the recent discovery of new natural isoenzymes with different biochemical properties, as well as the challenges in recombinant production render this enzyme particularly interesting for future biotechnological solutions. Therefore, we reviewed previous studies as well as current developments with biotechnological emphasis on new applications and the major remaining biotechnological challenge-the efficient recombinant production of horseradish peroxidase enzymes.

| S-EPMC4322221 | biostudies-literature

Stopped-flow spectrophotometric studies on the reaction of turkey liver xanthine dehydrogenase with reducing substrates.

Project description:The kinetics of reduction of turkey liver xanthine dehydrogenase by substrates were investigated by stopped-flow spectrophotometry. The results may be explained in terms of the known redox potentials of the various centres in the enzyme [Barber, Bray, Cammack & Coughlan (1977) Biochem. J. 163, 279-289]. They are, morover, consistent with the scheme [Olson, Ballou, Palmer & Massey (1974) J. Biol. Chem. 249, 4363-4382] in which reduction occurs in three consecutive steps, one molecule of substrate reacting with the active site at each step. First-order rate constants believed to correspond respectively to the combined first and second steps and to the third step in the reduction by excess of xanthine and of NADH were determined. The rates of reaction with these substrates in the combined first and second steps are independent of the degree of enzyme functionality.

| S-EPMC1184136 | biostudies-other

Induction of karyopherin ?1 expression by indole-3-acetic acid in auxin-treated or overproducing tobacco plants.

Project description:Macromolecules may transfer between the cytoplasm and the nucleus only through specific gates - the nuclear pore complexes (NPCs). Translocation of nucleic acids and large proteins requires the presence of a nuclear localization signal (NLS) within the transported molecule. This NLS is recognized by a class of soluble transport receptors termed karyopherins ? and beta. We previously characterized the expression pattern of the tomato karyopherin ? 1 (LeKAP?1) promoter in transformed tobacco plants. Expression of LeKAP?1 was mainly observed in growing tissues where cell division and extension is rapid. The expression pattern of LeKAP?1 resembled that of auxin-responsive genes. This led us to suggest that auxin participates in the regulation of LeKAP?1 expression. Here we characterized the correlation between auxin level and the activity of the LeKAP?1 promoter. To this end, transgenic tobacco plants carrying the GUS reporter gene under the control of the LeKAP?1 promoter were treated with various levels of exogenous auxin. We also studied transgenic plants in which we increased the endogenous levels of auxin. For this, we expressed in plants both the LeKAP?1 promoter-GUS reporter and the Agrobacterium tumefaciens iaaM gene, which increases the endogenous levels of auxin. The results indicate that the auxin indole-3-acetic acid (IAA) can induce LeKAP?1 expression. We also identified that the sites and levels of LeKAP?1 expression correlated with the endogenous pathways of polar auxin transport.

| S-EPMC3218478 | biostudies-literature

Tobacco mosaic virus-directed reprogramming of auxin/indole acetic acid protein transcriptional responses enhances virus phloem loading.

Project description:Vascular phloem loading has long been recognized as an essential step in the establishment of a systemic virus infection. In this study, an interaction between the replication protein of tobacco mosaic virus (TMV) and phloem-specific auxin/indole acetic acid (Aux/IAA) transcriptional regulators was found to modulate virus phloem loading in an age-dependent manner. Promoter expression studies show that in mature tissues TMV 126/183-kDa-interacting Aux/IAAs predominantly express and accumulate within the nuclei of phloem companion cells (CCs). Furthermore, CC Aux/IAA nuclear localization is disrupted upon infection with an interacting virus. In situ analysis of virus spread shows that the inability to disrupt Aux/IAA CC nuclear localization correlates with a reduced ability to load into the vascular tissue. Subsequent systemic movement assays also demonstrate that a virus capable of disrupting Aux/IAA localization is significantly more competitive at moving out of older plant tissues than a noninteracting virus. Similarly, CC expression and overaccumulation of a degradation-resistant Aux/IAA-interacting protein was found to inhibit TMV accumulation and phloem loading selectively in flowering plants. Transcriptional expression studies demonstrate a role for Aux/IAA-interacting proteins in the regulation of salicylic and jasmonic acid host defense responses as well as virus-specific movement factors, including pectin methylesterase, that are involved in regulating plasmodesmata size-exclusion limits and promoting virus cell-to-cell movement. Combined, these findings indicate that TMV directs the reprogramming of auxin-regulated gene expression within the vascular phloem of mature tissues as a means to enhance phloem loading and systemic spread.

| S-EPMC4868455 | biostudies-literature

indole-3-acetic acid (IAA) time course

Project description:Approximately 500 surface sterilized seeds of Arabidopsis seeds (ecotype: Col-0) were sterilely sown on filter disks overlaying solid ½ MS media 1% sucrose, stratified at 4C for 48 h and grown in darkness at 25C for 4 d. Seedlings were gently submerged by application to the plates of the different auxin solutions (made in ethanol carrier; 0.1% final concentration) and at the indicated times (20 min, 40 min, 60 min), the seedlings were lifted from the plate en mass and flash frozen in liquid nitrogen. Keywords: time-course

2003-10-12 | GSE664 | GEO

Inhibition of the indole-3-acetic acid-induced epinastic curvature in tobacco leaf strips by 2,4-dichlorophenoxyacetic acid.

Project description:It has been reported that auxin induces an epinastic growth response in plant leaf tissues. Leaf strips of tobacco (Nicotiana tabacum L. 'Bright Yellow 2') were used to study the effects of indole-3-acetic acid (IAA), the principal form of auxin in higher plants, and a synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), on epinastic leaf curvature. Incubation of leaf strips with 10 micro M IAA resulted in a marked epinastic curvature response. Unexpectedly, 2,4-D showed only a weak IAA-like activity in inducing epinasty. Interestingly, the presence of 2,4-D resulted in inhibition of the IAA-dependent epinastic curvature. In vivo Lineweaver-Burk kinetic analysis clearly indicated that the interaction between IAA and 2,4-D reported here is not a result of competitive inhibition. Using kinetic analysis, it was not possible to determine whether the mode of interaction between IAA and 2,4-D was non-competitive or uncompetitive. 2,4-D inhibits the IAA-dependent epinasty via complex and as yet unidentified mechanisms.

| S-EPMC4241065 | biostudies-literature

Electro-Oxidation and Simultaneous Determination of Indole-3-Acetic Acid and Salicylic Acid on Graphene Hydrogel Modified Electrode.

Project description:A selective and sensitive electrochemical sensor was developed for simultaneous detection of phytohormones indole-3-acetic acid (IAA) and salicylic acid (SA). The sensing interface was fabricated on a porous, three-dimensional networked graphene hydrogel (GH) modified glassy carbon electrode (GCE). The electrocatalytic behavior of IAA and SA on the surface of the modified electrode (GH/GCE) was investigated by cyclic voltammetry and linear sweep voltammetry. Results show that the oxidation reactions of IAA and SA occur at different potentials, which enable their simultaneous detection at the sensing interface. Under optimal conditions, the GH/GCE exhibited good selectivity and stability and its response, unaffected by various interferents, was linear in the range of 4 to 200 ?M of IAA and SA. The limit of detection (S/N = 3) achieved were 1.42 ?M for IAA and 2.80 ?M for SA. The sensor performance was validated by measuring for IAA and SA in real vegetable samples with satisfactory results.

| S-EPMC6960803 | biostudies-literature

A stopped-flow study of the cupric ion oxidation of adult-human haemoglobin.

Project description:The addition of excess Cu2+ to adult human haemoglobin leads to the production of alpha 2(2+) beta 2(3+), in both the oxy and deoxy forms of the protein. Stopped-flow studies of the oxidation process yields apparent second-order rate constants of 196M-1 X S-1 and 41M-1 X S-1 for the deoxy and oxy forms respectively. The rate of the deoxy-form oxidation is linearly dependent on [Cu2+], whereas that of the oxy form is rate-limited above 2 mM to 0.11 S-1. Arrhenius activation energies of the two processes are almost identical at 91 kJ X mol-1, as are the activation enthalpies of 89 kJ X mol-1. The activation entropies show small differences, being 31 entropy units and 48 entropy units for the oxy and deoxy forms respectively. ATP and glycerate 2,3-bisphosphate at saturating concentrations do not affect the rate of oxidation of the oxy form, but halve the rate found for the deoxy form. These data are discussed in terms of the previously proposed mechanism of oxidation in which slow Cu2+ binding is followed by rapid electron transfer.

| S-EPMC1162465 | biostudies-other

Detection of PRMT1 inhibitors with stopped flow fluorescence.

Project description:Protein arginine methyltransferases (PRMTs) are crucial epigenetic regulators in eukaryotic organisms that serve as histone writers for chromatin remodeling. PRMTs also methylate a variety of non-histone protein substrates to modulate their function and activity. The development of potent PRMT inhibitors has become an emerging and imperative research area in the drug discovery field to provide novel therapeutic agents for treating diseases and as tools to investigate the biological functions of PRMTs. PRMT1 is the major type I enzyme that catalyzes the formation of asymmetric dimethyl arginine, and PRMT1 plays important regulatory roles in signal transduction, transcriptional activation, RNA splicing, and DNA repair. Aberrant expression of PRMT1 is found in many types of cancers, pulmonary diseases, cardiovascular disease, diabetes, and renal diseases. PRMT1 is a highly promising target for therapeutic development. We created a stopped flow fluorescence-based assay for PRMT1 inhibitor detection and characterization that has the advantages of being homogeneous, nonradioactive, and mix-and-measure in nature, allowing for continuous measurement of the methylation reaction and its inhibition. To our knowledge, this is the first continuous assay for PRMT1 reaction detection and inhibitor characterization. The approach is not only capable of quantitatively determining the potency (IC50) of PRMT1 inhibitors but can also distinguish cofactor-competitive inhibitors, substrate-competitive inhibitors, and mixed-type inhibitors.

| S-EPMC5843908 | biostudies-literature

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