Figure 6.

Kinetics of transfer of heme from holo-IsdB-N2 to apo-IsdA-N1. The observed transfer rate (k_obs) varies hyperbolically with IsdA concentration, characteristic of a two-step reaction. Each point represents the mean and standard error of four replicates of the 2 μM IsdB-N2 to IsdA-N1 heme transfer experiment. Observed transfer rates at each concentration of IsdA-N1 were determined by plotting the change in absorbance at a given wavelength (418.9 nm for WT and 425.3 nm for M362L) vs time. The residuals for the curves are shown in the insets. (A) Transfer from WT holo-IsdB-N2 to apo-IsdA-N1. (B) Transfer from holo-IsdB-N2 M362L to apo-IsdA-N1.