Mössbauer study of 4-hydroxybutyryl-CoA dehydratase--probing the role of an iron-sulfur cluster in an overall non-redox reaction.

Abstract

4-Hydroxybutyryl-CoA dehydratase from Clostridium aminobutyricum catalyzes the dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA. Although dehydration is an overall non-redox reaction, the enzyme contains FAD and Fe-S clusters. Previous work has shown that the Fe-S clusters are difficult to reduce and therefore unlikely to be redox-active in catalysis. Here, Mössbauer spectroscopy has been used to characterise the Fe-S clusters in active as well as in air-inactivated enzyme. In zero magnetic field at 80 K and 4.2 K, the spectra of active dehydratase consisted mainly of one species (95%) with quadrupole splitting, deltaE(Q) = 1.00 mm s(-1) and isomer shift, delta = 0.43 mm s(-1). Magnetically perturbed Mössbauer spectra indicated a spin of zero. In the presence of 6 mM crotonyl-CoA, the spectra remained unchanged. Taken together, the data show that there are [4Fe-4S]2+ in the enzyme, most probably two clusters/homotetramer, that the four iron atoms in each cluster are coordinated in an identical fashion, and that there is no direct interaction with substrates. We therefore infer that the Fe-S clusters serve a structural rather than a catalytic role in 4-hydroxybutyryl-CoA dehydratase. In air-inactivated enzyme (10% residual activity), a new doublet appeared (58%) with deltaE(Q) = 0.72 mm s(-1), delta = 0.32 mm s(-1) and S = 0. The assignment of this subspectrum to [3Fe-4S]+ clusters, based on the typical Mössbauer parameters, is contradicted by the finding of spin zero for the species. One possible explanation could be spin-coupling of two [3Fe-4S]+ clusters in close proximity.

• Authors: U Müh, W Buckel, E Bill
• Journal: European journal of biochemistry (Eur J Biochem) Vol. 248 Issue 2 Pg. 380-4 (Sep 01 1997) ISSN: 0014-2956 [Print] England
• PMID: 9346292 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Sulfur
• Iron
• 4-hydroxybutyryl-CoA dehydratase
• Hydro-Lyases

Topics

• Air
• Enzyme Activation
• Hydro-Lyases (chemistry, metabolism)
• Iron (chemistry, metabolism)
• Oxidation-Reduction
• Spectroscopy, Mossbauer
• Sulfur (chemistry, metabolism)