PvdA flavin oxidation in the absence of ornithine. A. An oxygen-free solution containing 290 µM PvdA, 60 µM FAD, 360 µM NADPH in 100 mM potassium phosphate, pH 8.0 was mixed with an equal volume of the same buffer containing 1.3 mM oxygen at 22 °C. The spectra were recorded with a photodiode array. B. Representative absorbance-versus-time traces for absorbance at 390 nm (○) and 450 nm (●) were recorded using a photomultiplier tube. Enzyme, FAD, NADPH, and O2 mixing scheme as described in part A.