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Why does sulfite reductase employ siroheme?

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Abstract

Sulfite reductase (SiR) contains in the active site a unique assembly of siroheme and a [4Fe4S] cluster, linked by a cysteine residue. Siroheme is a doubly reduced variant of heme that is not used for a catalytic function in any other enzyme. We have used non-equilibrium Green's function methods coupled with density functional theory computations to explain why SiR employs siroheme rather than heme. The results show that direct, through vacuum, charge-transfer routes are inhibited when heme is replaced by siroheme. This ensures more efficient channelling of the electrons to the catalytic iron during the six-electron reduction of sulfite to sulfide, limiting potential side-reactions that could occur if the incoming electrons were delocalized onto the macrocyclic ring.

Graphical abstract: Why does sulfite reductase employ siroheme?

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Publication details

The article was received on 09 Jul 2019, accepted on 29 Oct 2019 and first published on 29 Oct 2019


Article type: Communication
DOI: 10.1039/C9CC05271B
Chem. Commun., 2019, Advance Article

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    Why does sulfite reductase employ siroheme?

    A. M. V. Brânzanic, U. Ryde and R. Silaghi-Dumitrescu, Chem. Commun., 2019, Advance Article , DOI: 10.1039/C9CC05271B

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