Sulfite reductase employs siroheme rather than heme due to higher efficiency in transferring electrons incoming from the [4Fe4S] cubane cofactor
- Date: Jan 15, 2026
- Time: 11:00 AM - 12:00 PM (Local Time Germany)
- Speaker: Adrian M.V. Brânzanic
- Interdisciplinary Research Institute on Bio-Nano Sciences, Babeș-Bolyai University, Cluj-Napoca, Romania. Raluca Ripan Institute for Research in Chemistry, Babeș-Bolyai University
- Location: MAx-Planck-Institut für Festkörperforschung
- Room: 4D2
- Host: Dep. of Electronic Structure Theory
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 used1 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.
References:
1A.M.V. Branzanic, U. Ryde, R. Silaghi-Dumitrescu, Chemical Communications, 2019, 55, 14047-14049.