Unusual kinetic properties of anionic tobacco peroxidase related to the mechanism of oxidation of indole-3-acetic acid |
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Authors: | I G Gazarian G A Ashby R N F Thorneley L M Lagrimini |
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Institution: | (1) Department of Chemical Enzymology, Chemical Faculty, Moscow State University, 119899 Moscow, GSP, Russia;(2) Nitrogen Fixation Laboratory, AFRC Institute of Plant Science Research, University of Sussex, Brighton, UK;(3) Department of Horticulture and Crop Science, Ohio State University, Columbus, OH |
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Abstract: | Anionic tobacco peroxidase (TOP) (mol wt 36 kDa, pI 3.5) was purified from transgenic tobacco plants with the yield of 60
mg/1 kg leaves. The enzyme exhibits unusual properties, i.e., Compound I is less reactive than Compound II. The enzyme was
investigated in oxidation of indole-3-acetic acid (IAA) oxidation by oxygen in the air. The aerobic steady-state spectral
studies reveal that Compound II is the key intermediate of the reaction mechanism. This was confirmed in the anaerobic stopped-flow
experiments. No reaction between the enzyme and IAA is observed under anaerobic conditions. The data obtained are interpreted
in terms of a ternary complex formation (ferric enzyme-IAA-oxygen) at the initiation step resulting in production of IAA radicals.
The latter interacts with the ferric enzyme and oxygen producing Compound II. The oxidative cycle involves the ferric enzyme
and Compound II, and is independent from the peroxidative one. |
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Keywords: | Compound I Compound II oxidative cycle reaction mechanism ternary complex hydrogen peroxide peroxidative cycle |
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