Indoleacetic Acid Oxidase: A Dual Catalytic Enzyme?

Abstract

The isolation of a unique enzyme capable of oxidizing indoleacetic acid, but devoid of peroxidase activity, has been reported for preparations from tobacco roots and commercial horseradish peroxidase. Experiments were made to verify these results using enzyme obtained from Betula leaves and commercial horseradish peroxidase. Both indoleacetic acid oxidase and guaiacol peroxidase activity appeared at 2.5 elution volumes from sulfoethyl-Sephadex. These results were obtained with both sources of enzyme. In no case was a separate peak of indoleacetic acid oxidase activity obtained at 5.4 elution volumes as reported for the tobacco enzyme using the same chromatographic system. Both types of activity, from both sources of enzyme, also eluted together during gel filtration. Successful column chromatography of Betula enzyme was dependent upon previous purification by membrane ultrafiltration. These results indicate indoleacetic acid oxidase activity and guaiacol peroxidase activity are dual catalytic functions of a single enzyme.The molecular "residence" of IAA oxidase activity is not known precisely. And this imprecision in our knowledge about IAA oxidase activity is a hindrance toward further understanding about the regulation of IAA levels in living plants.Up to now, three hypotheses, with varying amounts of substantiating evidence, have been reported in the scientific literature. The first considers that the two types of activity (i.e., IAA oxidase and peroxidase) are present on separable and distinct enzymes; the second considers that the two types of activity are resident on one enzyme (peroxidase) but with two active centers; and the third calls attention to the fact of peroxidase isoenzymes where one member of the family of isoenzymes may be the primary residence of IAA activity. These are examined briefly.The idea of separate enzymes was reported by Sequeira and Mineo (8). They had noted that fresh preparations (tobacco roots) lost IAA oxidase activity after several weeks in storage, whereas peroxidase activity was unchanged. Further, they found that thermal inactivation points and pH optima were different. Attempts to separate the two types of activity on columns of silica gel, carboxymethyl cellulose, diethylaminoethyl cellulose, and diethylaminoethyl Sephadex failed, but with SE'-Sephadex and 0.1 M eluting buffer they reported a Service, United States Department of Agriculture, Durham, major IAA oxidase peak (at 5.4 elution volumes) with little or no peroxidase activity from both tobacco root extracts and commercial HRPO.The belief that both types of activity reside with one enzyme (i.e., peroxidase) is more widely held. Evidence offered in support of this belief is mainly that both types of enzyme activity remain together through various stages of purification (7, 10), and also there is evidence that thermal inactivation is the same for both (7). The work of Siegel and Galston (9)

The effects of spraying methanol solution and drought stress on level of antioxidant enzyme activity, growth, biomass and yield of beans (<italic>Phaseolus vulgaris</italic> L.cv.COS16)

“…The Candlee and Scandalios method (1984) was used to measure catalase enzyme activity in root and leaf. Peroxidase enzyme activity in leaf and root was also measured by the Holy method (Hoyle, 1972). Dismutase superoxide enzyme activity of root and leaf was measured by the Beauchamp and Fridovich method (1971).…”

Activation of indole-3-acetic acid oxidase from horseradish and Prunus by phenols and H2O2

“…plant was freeze-dried and after removing the cortex and bast fibers, the white phloem and cambial layers were carefully separated from the xylem . After preparation of dry acetone powder from the phloem, 500 mg were incubated in 10 …”

“…However, in spite of many efforts, no clear picture of the identity of peroxidase and IAA-oxidase exists (10,26) and the variety of peroxidase catalysed reactions is puzzling . For example, the following oxidations are independent of the presence of H2 02 : Oxidation of dihydroxyfumaric acid, phenylacetaldehyde, oxaloacetate, triosereductone, naphthohydroquinone and indole-3-acetic acid (Eq .…”

Fenoles Solubles Totales Y Su Relacion Con La Inhibicion De La Rizogenesis en Estacas De Nothofagus Pumilio (Poepp. Et Endl.) Krasser

“…Muchos autores sugieren que AIA oxidasa es una peroxidasa, la cual, entre otras funciones celulares, controla el contenido endógeno de AIA (Phythoud & Buchala 1989;Beffa et al 1990;Rodríguez & Tamés 1983;Hoyle 1972).…”