Kinetic traces illustrating the complete suppression of both Tyr•
absorption signatures by ascorbate. The panels show “dropline”
treatments applied to the raw SF-abs data to extract the heights of the peaks
(A) at 416 nm (reference wavelengths of 406 and 426 nm),
arising from the first Tyr• and (B) at 410 nm (reference
wavelengths of 404 and 416 nm), arising from the second Tyr•. The
reactions were carried out by mixing an anoxic solution of 0.65 mM protein, 0.58
mM Fe(NH4)2(SO4)2, 0.58 mM
2, 5.0 mM 2OG, and (solely for the blue traces) 1.0 mM
ascorbate at 5°C with an equal volume of O2-saturated
buffer.