Effects of the loss of the axial tyrosine ligand of the low-spin heme of MauG on its physical properties and reactivity

► A Y294K mutation results in loss rather than replacement of the axial heme ligand provided by Tyr294. ► A Y294K mutation alters spectroscopic and redox properties of both hemes of MauG. ► Y294K MauG forms a high valent compound I-like species rather than a bis-Fe(IV) species. ► Y294K MauG is competent in long range electron transfer but has lost TTQ biosynthesis activity.