MauG is an enzyme responsible for the maturation of the tryptophan tryptophylquinone (TTQ) cofactor of methylamine dehydrogenase (MADH) from an inactive precursor protein (preMADH). The reaction involves a six-electron oxidation of the substrate and requires the formation of an unusual high-valent di-heme species, an Fev equivalent referred to as bis-Feiv. This species can be formed either by reaction of H2O2 with the diferric form or activation of O2 by the diferrous form of MauG. Stabilization of bis-Feiv and catalysis involves ultrafast electron transfer between MauG hemes and efficient hole hopping through a series of Trp residues connecting the enzyme and substrate. MauG thus provides an excellent system to study the mechanisms of long-range electron transfer and radical stabilization that are essential for critical biological processes.