Fig 4. Both FecB and FecB2 bind heme, while FecB preferentially binds Fe-cMB compared to FecB2.
Representative fluorescent emission intensities at 335 nm after excitation at 280 nm of 100 nM FecB (left panels) and 100 nM FecB2 (right panels) with increasing concentrations of A. heme and B. Fe-cMB. Notably the experiments in (A) were performed with tagless proteins. Curves were fit using Eq 1 and affinities (Kd) are included for each titration. In (A) FecB binds heme with a higher affinity than FecB2, in contrast to (B) showing that FecB binds Fe-cMB whereas FecB2 does not.