Inactivation of 4-Oxalocrotonate Tautomerase by 5-Halo-2-hydroxy-2,4-pentadienoates
- Univ. of Texas, Austin, TX (United States)
5-Halo-2-hydroxy-2,4-pentadienoates (5-halo-HPDs) are reportedly generated in the bacterial catabolism of halogenated aromatic hydrocarbons by the meta-fission pathway. The 5-halo-HPDs, where the halogen can be bromide, chloride, or fluoride, result in the irreversible inactivation of 4-oxalocrotonate tautomerase (4-OT), which precedes the enzyme that generates them. The loss of activity is due to the covalent modification of the nucleophilic amino-terminal proline. Mass spectral and crystallographic analysis of the modified enzymes indicates that inactivation of 4-OT by 5-chloro- and 5-bromo-2-hydroxy-2,4-pentadienoate follows a mechanism different from that for the inactivation of 4-OT by 5-fluoro-2-hydroxy-2,4-pentadienoate. The 5-chloro and 5-bromo derivatives undergo 4-OT-catalyzed tautomerization to their respective α,β-unsaturated ketones followed by attack at C5 (by the prolyl nitrogen) with concomitant loss of the halide. For the 5-fluoro species, the presence of a small amount of the α,β-unsaturated ketone could result in a Michael addition of the prolyl nitrogen to C4 followed by protonation at C3. The fluoride is not eliminated. Here, these observations suggest that the inactivation of 4-OT by a downstream metabolite could hamper the efficacy of the pathway, which is the first time that such a bottleneck has been reported for the meta-fission pathway.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- National Inst. of Health; Robert A. Welch Foundation
- OSTI ID:
- 1433697
- Journal Information:
- Biochemistry, Journal Name: Biochemistry Journal Issue: 6 Vol. 57; ISSN 0006-2960
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- ENGLISH
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