Direct Participation of Potassium Ion in the Catalysis of Coenzyme B12-Dependent Diol Dehydratase.
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概要
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The direct ion-dipolar interactions between potassium ion (K+) and the two hydroxyl groups of the substrate are the most striking feature of the crystal structure of coenzyme B12-dependent diol dehydratase. We carried out density-functional-theory computations to determine whether K+ can assist the 1, 2-shift of the hydroxyl group in the substratederived radical. Between a stepwise abstraction/recombination reaction proceeding via a direct hydroxide abstraction by K+ and a concerted hydroxyl group migration assisted by K+, only a transition state for the latter concerted mechanism was found from our computations. The barrier height for the transition state from the complexed radical decreases by only 2.3 kcal/mol upon coordination of the migrating hydroxyl group to K+, which corresponds to a 42-fold rate acceleration at 37°C. The net binding energy upon replacement of the K+-bound water for substrate was calculated to be 10.7 kcal/mol. It can be considered that such a large binding energy is at least partly used for the substrateinduced conformational changes in the enzyme that trigger the homolytic cleavage of the Co-C bond of the coenzyme and the subsequent catalysis by a radical mechanism. We propose here a new mechanism for diol dehydratase in which K+ plays a direct role in the catalysis.
- 社団法人 日本生化学会の論文
著者
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Toraya Tetsuo
Department Of Bioscience And Biotechnology Faculty Of Engineering Okayama University
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Eda Masataka
Department Of Molecular Engineering Kyoto University
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Yoshizawa Kazunari
Department Of Molecular Engineering Graduate School Of Engineering Kyoto University
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Toraya Tetsuo
Department of Bioscience and Biotechnology, Faculty of Engineering, Ohayama University
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Yamabetl Tokio
Department of Molecular Engineering, Kyoto University
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