Andreas Ioannis Karsisiotis

Exogenous ligand binding to ferricyt can be used as a diagnostic probe to assess the lability of the Met80 ligand. On mixing N − with WT or G41S H-ferricyt an optical transition was observed (Fig. 2A) with differing time courses for the two proteins, as shown in the inset to Fig. 2A. Such an optical transition reflects the dissociation of the Met80 ligand from the heme and the binding of N − in its place.

Author contributions: C.M. and M.N. contributed equally to this work. AM conceived and coordinated the study and wrote the paper. CM and MN contributed substantially to conception and design, acquisition and analysis of data, and also to writing the article. OJ, NW, MD, AIK contributed significantly to acquisition of data. GCKR, CD, CR contributed decidedly to design, analysis and interpretation of NMR experiments, and also drafting the article.