Fig. 7. Flash-induced absorption changes at 540 nm (mainly due to Trp˙) on a μs/ms timescale for WT MmCPDII (44.0 μM before dilution by buffer containing cysteine) in the absence and in the presence of cysteine as reducing agent (signals of samples with cysteine are normalized to the amplitude of the cysteine-free sample at t → 0 for better visualization of the effect of cysteine on the kinetics of Trp˙ reduction). Reduction of Trp˙ (and Tyr˙) radical(s) by cysteine stabilizes the FAD˙^– anion radical, most of which is then protonated to FADH˙ with a time constant of 630 ms. Inset: the disappearance of FAD˙^– was observed at 380 nm and the corresponding formation of FADH˙ at 610 nm. Samples were excited at 470 nm by 5 ns pulses of E ∼ 2 mJ per cm². Except for the 610 nm trace in the inset, which is an average of 3 signals, all other traces are results of single-flash experiments.