FIGURE 4.

The effect of heme on iron release from E. coli BFR followed by a dithionite/FMN-ferrozine assay. A, plots of ΔA_{562 nm} as a function of time following the addition of 100 μm sodium dithionite and 75 μm FMN to either wild-type BFR containing 5 hemes/24-mer or to heme-free M52H BFR. Both BFRs (0.05 μm) contained ∼1200 irons/protein in MBS, 1 mm ferrozine, pH 7. The release reaction was conducted at 15 °C. B, apparent rate constants, obtained from fitting the data in A (and similar experiments in which FMN concentration was varied), plotted as a function of FMN concentration. C, the concentration of iron detected as the [Fe(II)(ferrozine)₃]⁴⁻ complex at the end point of each release reaction as a function of FMN concentration. Error bars, S.D.