Direct participation of potassium ion in the catalysis of Coenzyme B12-dependent diol dehydratase

Tetsuo Toraya, Kazunari Yoshizawa, Masataka Eda, Tokio Yamabe

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40 Citations (Scopus)


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 substrate-derived 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 substrate-induced 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.

Original languageEnglish
Pages (from-to)650-654
Number of pages5
JournalJournal of Biochemistry
Issue number4
Publication statusPublished - 1999
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biochemistry


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