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Investigation of acid-base catalysis in the extradiol and intradiol catechol dioxygenase reactions using a broad specificity mutant enzyme and model chemistry
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Brivio, Michela, Schlosrich, Janne, Ahmad, Mark, Tolond, Caroline and Bugg, Tim (2009) Investigation of acid-base catalysis in the extradiol and intradiol catechol dioxygenase reactions using a broad specificity mutant enzyme and model chemistry. Organic & Biomolecular Chemistry, Vol.7 (No.7). pp. 1368-1373. doi:10.1039/b821559f
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Official URL: http://dx.doi.org/10.1039/b821559f
Abstract
The extradiol and intradiol catechol dioxygenase reaction mechanisms proceed via a common proximal hydroperoxide intermediate, which is processed via different Criegee 1,2-rearrangements. An R215W mutant of extradiol dioxygenase MhpB, able to produce a mixture of extradiol and intradiol cleavage products, was analysed at pH 5.2-8.6, and the yield of extradiol product was found to be highly pH-dependent, whereas the yield of intradiol product was pH-independent. The acid-base chemistry of a biomimetic reaction for extradiol oxidative catechol cleavage was also investigated, using 1,4,7-triazacyclononane, FeCl2, and pyridine in methanol, in which pyridine is proposed to act as both a general base and (in protonated form) a general acid. Kinetic experiments using a range of meta-and para-substituted pyridines gave a Bronsted plot of log(v) vs. pK(a) showing a bell-shaped plot. Oxidative catechol cleavage by a pyridine-monosubstituted beta-cyclodextrin in the presence of TACN and FeCl2 in methanol yielded only intradiol cleavage products. It is therefore proposed that bifunctional acid-base catalysis is required for iron (II)-dependent extradiol catechol cleavage, whereas the rate-determining step for intradiol catechol cleavage does not involve acid-base catalysis.
| Item Type: | Journal Article | ||||
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| Subjects: | Q Science > QD Chemistry Q Science > QP Physiology |
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| Divisions: | Other > Institute of Advanced Study Faculty of Science > Chemistry |
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| Library of Congress Subject Headings (LCSH): | Acid-base chemistry, Metalloenzymes, Catechol, Escherichia coli | ||||
| Journal or Publication Title: | Organic & Biomolecular Chemistry | ||||
| Publisher: | Royal Society of Chemistry | ||||
| ISSN: | 1477-0520 | ||||
| Official Date: | 2009 | ||||
| Dates: |
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| Volume: | Vol.7 | ||||
| Number: | No.7 | ||||
| Number of Pages: | 6 | ||||
| Page Range: | pp. 1368-1373 | ||||
| DOI: | 10.1039/b821559f | ||||
| Status: | Peer Reviewed | ||||
| Publication Status: | Published | ||||
| Funder: | Erasmus Mundus (Program) |
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