Catalytic reaction of cytokinin dehydrogenase: preference for quinones as electron acceptors
Language English Country England, Great Britain Media print
Document type Comparative Study, Journal Article, Research Support, Non-U.S. Gov't
PubMed
14965342
PubMed Central
PMC1224151
DOI
10.1042/bj20031813
PII: BJ20031813
Knihovny.cz E-resources
- MeSH
- Aldehydes metabolism MeSH
- Quinones metabolism MeSH
- Cytokinins metabolism MeSH
- Electrochemistry MeSH
- Flavin-Adenine Dinucleotide metabolism MeSH
- Catalysis MeSH
- Kinetics MeSH
- Zea mays enzymology MeSH
- Oxidation-Reduction MeSH
- Oxidoreductases chemistry metabolism MeSH
- Recombinant Proteins metabolism MeSH
- Plant Proteins chemistry metabolism MeSH
- Substrate Specificity MeSH
- Protein Structure, Tertiary MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Comparative Study MeSH
- Names of Substances
- Aldehydes MeSH
- Quinones MeSH
- cytokinin oxidase MeSH Browser
- Cytokinins MeSH
- Flavin-Adenine Dinucleotide MeSH
- Oxidoreductases MeSH
- Recombinant Proteins MeSH
- Plant Proteins MeSH
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 (k(red)=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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