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Mossbauer Studies of Beef Heart Aconitase: Evidence for Facile Interconversions of Iron-Sulfur Clusters

Thomas A. Kent, Jean-Luc Dreyer, Mary Claire Kennedy, Boi Hanh Huynh, Mark H. Emptage, Helmut Beinert and Eckard Munck
Proceedings of the National Academy of Sciences of the United States of America
Vol. 79, No. 4, [Part 1: Biological Sciences] (Feb. 15, 1982), pp. 1096-1100
Stable URL: http://www.jstor.org/stable/11986
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Mossbauer Studies of Beef Heart Aconitase: Evidence for Facile Interconversions of Iron-Sulfur Clusters
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Abstract

Beef heart aconitase, isolated under aerobic conditions, has been studied with Mossbauer and EPR spectroscopy. In the oxidized state, the enzyme exhibits an EPR signal at g = 2.01. The Mossbauer data show that this signal is associated with a 3Fe cluster. In dithionite-reduced aconitase, the 3Fe cluster, probably of the [3Fe-3S] type, is in a paramagnetic state of integer electronic spin (S = 2); the Mossbauer spectra exhibit all the unique features reported for proteins with 3Fe clusters. On activation of aconitase with ferrous ion, the paramagnetic 3Fe cluster of dithionite-reduced enzyme is converted into a diamagnetic (S = 0) form. Activation studies with iron enriched in either 57Fe or 56Fe suggest that activation transforms the 3Fe cluster into a center that has a [4Fe-4S] core. This conclusion is supported by the observation that EPR signals characteristic of reduced [4Fe-4S] clusters can be elicited under appropriate conditions. It has frequently been assumed that the activation of aconitase with Fe2+ produces an active site containing a single ferrous ion. The data reported here suggest that a ferrous ion is used to rebuild a [4Fe-4S] cluster.

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