Carbonic anhydrase (CA) is a ubiquitous metalloenzyme with a Zn cofactor coordinated to trigonal histidine imidazole moieties in a tetrahedral geometry. Removal of the Zn cofactor in CA and subsequent binding of Ir afforded CA[Ir]. Under mild and neutral conditions (30 °C, pH 7), CA[Ir] exhibited water‐oxidizing activity with a turnover frequency (TOF) of 39.8 min⁻¹, which is comparable to those of other Ir‐based molecular catalysts. Coordination of Ir to the apoprotein of CA is thermodynamically preferred and is associated with an exothermic energy change (ΔH) of −10.8 kcal mol⁻¹, which implies that the CA apoprotein is stabilized by Ir binding. The catalytic oxygen‐evolving activity of CA[Ir] is displayed only if Ir is bound to CA, which functions as an effective biological scaffold that activates the Ir center for catalysis. The results of this study indicate that the histidine imidazoles at the CA active site could be exploited as beneficial biological ligands to provide unforeseen biochemical activity by coordination to a variety of transition‐metal ions.

中文翻译：

---

铱修饰的碳酸酐酶催化水氧化

碳酸酐酶（CA）是一种普遍存在的金属酶，具有Zn辅助因子，与四面体几何结构中的三角组氨酸咪唑部分相协调。去除CA中的Zn辅助因子并随后与Ir结合，得到CA [Ir]。在中性和中性条件下（30°C，pH 7），CA [Ir]表现出水氧化活性，周转频率（TOF）为39.8 min ^-1，与其他基于Ir的分子催化剂相当。Ir与CA载脂蛋白的配位在热力学上是优选的，并且与-10.8 kcal mol ^-1的放热能变化（ΔH）有关，这表明CA脱辅基蛋白通过Ir结合得以稳定。仅当Ir与CA结合时，CA [Ir]的催化氧释放活性才显示出来，CA是有效的生物支架，可激活Ir中心进行催化。这项研究的结果表明，CA活性位点上的组氨酸咪唑可被用作有益的生物配体，通过与多种过渡金属离子配位提供不可预见的生化活性。