Plant Adenosine 5′-Phosphosulfate Reductase Is a Novel Iron-Sulfur Protein

Stanislav Kopriva, Thomas Büchert, Günter Fritz, Marianne Suter, Markus Weber, Rüdiger Benda, Johann Schaller, Urs Feller, Peter Schürmann, Volker Schünemann, Alfred X. Trautwein, Peter M.H. Kroneck, Christian Brunold


Adenosine 5'-phosphosulfate reductase (APR) catalyzes the two-electron reduction of adenosine 5'-phosphosulfate to sulfite and AMP, which represents the key step of sulfate assimilation in higher plants. Recombinant APRs from both Lemna minor and Arabidopsis thaliana were overexpressed in Escherichia coli and isolated as yellow-brown proteins. UV-visible spectra of these recombinant proteins indicated the presence of iron-sulfur centers, whereas flavin was absent. This result was confirmed by quantitative analysis of iron and acid-labile sulfide, suggesting a [4Fe-4S] cluster as the cofactor. EPR spectroscopy of freshly purified enzyme showed, however, only a minor signal at g = 2.01. Therefore, Mossbauer spectra of (57)Fe-enriched APR were obtained at 4.2 K in magnetic fields of up to 7 tesla, which were assigned to a diamagnetic [4Fe-4S](2+) cluster. This cluster was unusual because only three of the iron sites exhibited the same Mossbauer parameters. The fourth iron site gave, because of the bistability of the fit, a significantly smaller isomer shift or larger quadrupole splitting than the other three sites. Thus, plant assimilatory APR represents a novel type of adenosine 5'-phosphosulfate reductase with a [4Fe-4S] center as the sole cofactor, which is clearly different from the dissimilatory adenosine 5'-phosphosulfate reductases found in sulfate reducing bacteria.
Original languageEnglish
JournalJournal of Biological Chemistry
Issue number46
Pages (from-to)42881-42886
Number of pages6
Publication statusPublished - 16.11.2001


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