Materials and Reagents

1. Quinone reductase purified from Escherichia coli (E. coli) by Ni-NTA chromatography as described in Mancini et al. (2015).
   
2. p-Benzoquinone (Sigma-Aldrich, catalog number: B10358 )
   Note: optionally other quinone substrates like 1, 4-penzoquinone, 2-methyl-1, 4-benzoquinone, 2, 5-dimethyl-1, 4-benzoquinone, menadione, naphthoquinone, or 2, 6-dichloro-1, 4-benzoquinone, all available from Sigma-Aldrich.
   
3. 50 mM NADPH in water; prepare on the day of use (Sigma-Aldrich, catalog number: N5130 )
   
4. 20 mM Tris-Cl buffer (pH 7.5)
   
5. Flavin mononucleotide (Sigma-Aldrich, catalog number: F1392 )
   
6. p-Benzoquinone (see Recipes)
   
7. NADPH (see Recipes)
   
8. 20 mM Tris-Cl (see Recipes)
   
9. 100 µM flavin mononucleotide (see Recipes)
   

Equipment

1. Thermostated spectrophotometer (Shimadzu, model: UV2600 or similar)

Procedure