Fig. 5.

The transient tyrosyl radical of SynFtn. (A) EPR signal due to a tyrosyl radical in SynFtn frozen 12 s after initiating iron oxidation (iron added at 80 Fe²⁺/Ftn). The simulation parameters are reported in SI Appendix, Table S4. (B) Intensity of the tyrosyl radical signal at increasing iron loading in samples of 4.17 µM SynFtn in 100 mM Mes, pH 6.5, frozen 10 s after mixing. Response from the apo protein and protein loaded with 80 Fe²⁺ per Ftn are shown in black, and intermediate loadings (12, 24, and 48 equivalents of Fe²⁺) are shown in gray. (C) Increase in signal intensity due to the radical at approximately g = 2 in samples of 4.17 µM SynFtn frozen 50–365 ms after mixing with 72 equivalents of Fe²⁺. Thick traces are the shortest (50 ms) and longest (365 ms) aging times shown. Traces at intermediate freezing times are shown in gray.