Probing Bis‐FeIV MauG: Experimental Evidence for the Long‐Range Charge‐Resonance Model

The biosynthesis of tryptophan tryptophylquinone, a protein‐derived cofactor, involves a long‐range reaction mediated by a bis‐Fe^IV intermediate of a diheme enzyme, MauG. Recently, a unique charge‐resonance (CR) phenomenon was discovered in this intermediate, and a biological, long‐distance CR model was proposed. This model suggests that the chemical nature of the bis‐Fe^IV species is not as simple as it appears; rather, it is composed of a collection of resonance structures in a dynamic equilibrium. Here, we experimentally evaluated the proposed CR model by introducing small molecules to, and measuring the temperature dependence of, bis‐Fe^IV MauG. Spectroscopic evidence was presented to demonstrate that the selected compounds increase the decay rate of the bis‐Fe^IV species by disrupting the equilibrium of the resonance structures that constitutes the proposed CR model. The results support this new CR model and bring a fresh concept to the classical CR theory.