The catalytic reaction of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) was studied in detail using the recombinant flavoenzyme from maize. Determination of the redox potential of the covalently linked flavin cofactor revealed a relatively high potential dictating the type of electron acceptor that can be used by the enzyme. Using 2,6-dichlorophenol indophenol, 2,3-dimethoxy-5-methyl-1,4-benzoquinone or 1,4-naphthoquinone as electron acceptor, turnover rates with N6-(2-isopentenyl)adenine of approx. 150 s−1 could be obtained. This suggests that the natural electron acceptor of the enzyme is quite probably a p-quinone or similar compound. By using the stopped-flow technique, it was found that the enzyme is rapidly reduced by N6-(2-isopentenyl)adenine (kred=950 s−1). Re-oxidation of the reduced enzyme by molecular oxygen is too slow to be of physiological relevance, confirming its classification as a dehydrogenase. Furthermore, it was established for the first time that the enzyme is capable of degrading aromatic cytokinins, although at low reaction rates. As a result, the enzyme displays a dual catalytic mode for oxidative degradation of cytokinins: a low-rate and low-substrate specificity reaction with oxygen as the electron acceptor, and high activity and strict specificity for isopentenyladenine and analogous cytokinins with some specific electron acceptors.
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May 15 2004
Catalytic reaction of cytokinin dehydrogenase: preference for quinones as electron acceptors Available to Purchase
Jitka FRÉBORTOVÁ;
Jitka FRÉBORTOVÁ
*Laboratory of Growth Regulators, Faculty of Science, Palacký University/Institute of Experimental Botany of the Academy of Science, Šlechtitelů 11, 783 71 Olomouc, Czech Republic
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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Marco W. FRAAIJE;
Marco W. FRAAIJE
†Laboratory of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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Petr GALUSZKA;
Petr GALUSZKA
‡Division of Molecular Biology, Faculty of Science, Palacký University, Šlechtitelů 11, 783 71 Olomouc, Czech Republic
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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Marek ŠEBELA;
Marek ŠEBELA
§Department of Biochemistry, Faculty of Science, Palacký University, Šlechtitelů 11, 783 71 Olomouc, Czech Republic
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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Pavel PEČ;
Pavel PEČ
§Department of Biochemistry, Faculty of Science, Palacký University, Šlechtitelů 11, 783 71 Olomouc, Czech Republic
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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Jan HRBÁČ;
Jan HRBÁČ
‖Department of Physical Chemistry, Faculty of Science, Palacký University, tř. Svobody 26, 771 46 Olomouc, Czech Republic
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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Ondřej NOVÁK;
Ondřej NOVÁK
*Laboratory of Growth Regulators, Faculty of Science, Palacký University/Institute of Experimental Botany of the Academy of Science, Šlechtitelů 11, 783 71 Olomouc, Czech Republic
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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Kristin D. BILYEU;
Kristin D. BILYEU
‖Department of Physical Chemistry, Faculty of Science, Palacký University, tř. Svobody 26, 771 46 Olomouc, Czech Republic
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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James T. ENGLISH;
James T. ENGLISH
**Department of Plant Microbiology and Pathology, University of Missouri, Columbia, MO 65211, U.S.A.
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
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Ivo FRÉBORT
Ivo FRÉBORT
1
‡Division of Molecular Biology, Faculty of Science, Palacký University, Šlechtitelů 11, 783 71 Olomouc, Czech Republic
¶USDA/ARS, 210 Waters Hall, Columbia, MO 65211, U.S.A.
1To whom correspondence should be addressed (e-mail [email protected]).
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Publisher: Portland Press Ltd
Received:
November 26 2003
Revision Received:
January 15 2004
Accepted:
February 13 2004
Accepted Manuscript online:
February 13 2004
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London ©2004
2004
Biochem J (2004) 380 (1): 121–130.
Article history
Received:
November 26 2003
Revision Received:
January 15 2004
Accepted:
February 13 2004
Accepted Manuscript online:
February 13 2004
Citation
Jitka FRÉBORTOVÁ, Marco W. FRAAIJE, Petr GALUSZKA, Marek ŠEBELA, Pavel PEČ, Jan HRBÁČ, Ondřej NOVÁK, Kristin D. BILYEU, James T. ENGLISH, Ivo FRÉBORT; Catalytic reaction of cytokinin dehydrogenase: preference for quinones as electron acceptors. Biochem J 15 May 2004; 380 (1): 121–130. doi: https://doi.org/10.1042/bj20031813
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