Enzyme activity assay of PdcG. (a) Absorbance from 270 nm to 320 nm in the absence of His6-PdcG; (b) Spectral changes during oxidation of 4-HS by His6-PdcDE. The spectra were recorded a total of five times over a five minute period (marked 1-5). The arrow indicates the direction of spectral changes. (c) Spectral changes at 320 nm during metabolism of HQ by purified His6-PdcDE and oxidation of 4-HS by purified His6-PdcG. The arrow indicates when NAD+ was added.