Figure 3: Biochemical and spectroscopic analysis.

(a) Difference titration of TtENR with p-hydroxybenzaldehyde. The determined Kd value was 25 μM. The insert shows the difference ultraviolet–visible spectra. (b) Double-reciprocal plot of initial rate measurements with PhENR as a function of NADH at 20 (filled circles), 30 (open circles), 50 (filled triangles), 90 (open triangles) and 150 (filled squares) μM of 1,4-benzoquinone. (c) Ultraviolet–visible spectra of anaerobic photoreduction of PhENR (upper panel) and TtENR (lower panel), where the peak at 402 nm indicates the presence of the red radical species.