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Mössbauer and EPR studies of activated aconitase: development of a localized valence state at a subsite of the [4Fe-4S] cluster on binding of citrate.
Proc Natl Acad Sci U S A. 1983 Aug; 80(15):4674-8.PN

Abstract

During activation of aconitase a ferrous ion is incorporated into a [3Fe-4S] cluster to yield a structure with a [4Fe-4S] core. Using 57Fe or 56Fe for activation we have studied with Mössbauer spectroscopy the beef heart enzyme in the presence of citrate. Our studies show that the environment of one iron site (Fea) of the [4Fe-4S] cluster is drastically altered in the presence of citrate. Fea is the iron acquired during activation of aconitase. In the oxidized [4Fe-4S]2+ state two species with enzyme-bound substrate are observed, whereas only one is observed in the reduced [4Fe-4S]+ state. The Mössbauer parameters of Fea reveal that the site has acquired substantial high-spin ferrous character. This is most pronounced in the 1+ state where at Fea the cluster exhibits a localized valence state. The dramatic increase of the isomer shift upon substrate binding strongly suggests that the ligand environment of Fea has become at least five-coordinate and that the cluster may function as a Lewis acid. In the absence of citrate the EPR spectra of the active [4Fe-4S]+ enzyme (g1,2,3 = 2.06, 1.93, 1.86) show no hyperfine broadening in the presence of H2 17O. However, in the presence of citrate (g1,2,3 = 2.04, 1.85, 1.78) sizable transferred hyperfine interactions are observed; under the experimental conditions the hydroxyl groups of citrate and isocitrate as well as water are labeled with 17O. We did not detect broadening by 17O-labeled carboxyl groups of citrate in H2 16O. Implications for the mechanism of aconitase are discussed.

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Authors

Emptage MH
No affiliation info available
Kent TA
No affiliation info available
Kennedy MC
No affiliation info available
Beinert H
No affiliation info available
Münck E
No affiliation info available

MeSH

Aconitate HydrataseAnimalsBinding SitesCattleCitratesCitric AcidElectron Spin Resonance SpectroscopyEnzyme ActivationIron-Sulfur ProteinsKineticsMetalloproteinsMitochondria, HeartProtein BindingSpectrum Analysis

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

6308639

Citation

Emptage, M H., et al. "Mössbauer and EPR Studies of Activated Aconitase: Development of a Localized Valence State at a Subsite of the [4Fe-4S] Cluster On Binding of Citrate." Proceedings of the National Academy of Sciences of the United States of America, vol. 80, no. 15, 1983, pp. 4674-8.
Emptage MH, Kent TA, Kennedy MC, et al. Mössbauer and EPR studies of activated aconitase: development of a localized valence state at a subsite of the [4Fe-4S] cluster on binding of citrate. Proc Natl Acad Sci U S A. 1983;80(15):4674-8.
Emptage, M. H., Kent, T. A., Kennedy, M. C., Beinert, H., & Münck, E. (1983). Mössbauer and EPR studies of activated aconitase: development of a localized valence state at a subsite of the [4Fe-4S] cluster on binding of citrate. Proceedings of the National Academy of Sciences of the United States of America, 80(15), 4674-8.
Emptage MH, et al. Mössbauer and EPR Studies of Activated Aconitase: Development of a Localized Valence State at a Subsite of the [4Fe-4S] Cluster On Binding of Citrate. Proc Natl Acad Sci U S A. 1983;80(15):4674-8. PubMed PMID: 6308639.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Mössbauer and EPR studies of activated aconitase: development of a localized valence state at a subsite of the [4Fe-4S] cluster on binding of citrate. AU - Emptage,M H, AU - Kent,T A, AU - Kennedy,M C, AU - Beinert,H, AU - Münck,E, PY - 1983/8/1/pubmed PY - 1983/8/1/medline PY - 1983/8/1/entrez SP - 4674 EP - 8 JF - Proceedings of the National Academy of Sciences of the United States of America JO - Proc Natl Acad Sci U S A VL - 80 IS - 15 N2 - During activation of aconitase a ferrous ion is incorporated into a [3Fe-4S] cluster to yield a structure with a [4Fe-4S] core. Using 57Fe or 56Fe for activation we have studied with Mössbauer spectroscopy the beef heart enzyme in the presence of citrate. Our studies show that the environment of one iron site (Fea) of the [4Fe-4S] cluster is drastically altered in the presence of citrate. Fea is the iron acquired during activation of aconitase. In the oxidized [4Fe-4S]2+ state two species with enzyme-bound substrate are observed, whereas only one is observed in the reduced [4Fe-4S]+ state. The Mössbauer parameters of Fea reveal that the site has acquired substantial high-spin ferrous character. This is most pronounced in the 1+ state where at Fea the cluster exhibits a localized valence state. The dramatic increase of the isomer shift upon substrate binding strongly suggests that the ligand environment of Fea has become at least five-coordinate and that the cluster may function as a Lewis acid. In the absence of citrate the EPR spectra of the active [4Fe-4S]+ enzyme (g1,2,3 = 2.06, 1.93, 1.86) show no hyperfine broadening in the presence of H2 17O. However, in the presence of citrate (g1,2,3 = 2.04, 1.85, 1.78) sizable transferred hyperfine interactions are observed; under the experimental conditions the hydroxyl groups of citrate and isocitrate as well as water are labeled with 17O. We did not detect broadening by 17O-labeled carboxyl groups of citrate in H2 16O. Implications for the mechanism of aconitase are discussed. SN - 0027-8424 UR - https://www.unboundmedicine.com/medline/citation/6308639/M��ssbauer_and_EPR_studies_of_activated_aconitase:_development_of_a_localized_valence_state_at_a_subsite_of_the_[4Fe_4S]_cluster_on_binding_of_citrate_ L2 - http://www.pnas.org/cgi/pmidlookup?view=long&pmid=6308639 DB - PRIME DP - Unbound Medicine ER -