Department of Chemistry, Babes-Bolyai University, Cluj-Napoca, Romania.
Department of Theoretical Chemistry, Lund University, Lund, Sweden.
Chem Commun (Camb). 2019 Dec 4;55(93):14047-14049. doi: 10.1039/c9cc05271b. Epub 2019 Nov 6.
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.
亚硫酸还原酶 (SiR) 在其活性位点含有独特的组装体，由一个半胱氨酸残基连接的亚血红素和一个 [4Fe4S] 簇。亚血红素是血红素的一种双重还原变体，在任何其他酶中都不用于催化功能。我们使用非平衡格林函数方法结合密度泛函理论计算来解释为什么 SiR 使用亚血红素而不是血红素。结果表明，当血红素被亚血红素取代时，直接通过真空的电荷转移途径受到抑制。这确保了在六电子将亚硫酸盐还原为硫化物的过程中，电子更有效地传递到催化铁上，限制了如果传入的电子被分散到大环上可能发生的潜在副反应。
