Purification and properties of a NAD(P)H:flavin oxidoreductase from the luminous bacterium, Beneckea harveyi

A NAD(P)H:flavin oxidoreductase, which produces FMNH2, one of the substrates for the luciferase reaction in bioluminescent bacteria, has been purified with the aid of affinity chromatography on epsilon-aminohexanoyl-FMN-Sepharose. The purified enzyme, isolated from Beneckea harveyi, had a specific activity of 89 mumol of NADH oxidized/min/mg of protein at 23 degrees in the presence of saturating FMN and NADH and appeared homogeneous by several criteria on polyacrylamide gel electrophoresis. A molecular weight of 24,000 was estimated both by gel filtration and and sodium dodecyl sulfate gel electrophoresis indicating that the enzyme is composed of a single polypeptide chain. Kinetic studies showed that the higher specificity of the enzyme for NADH than NADPH and for riboflavin and FMN than FAD was primarily due to variations in the Michaelis constants for the different substrates. Initial velocity studies with all pairs of substrates gave intersecting patterns supporting a sequential mechanism for the NAD(P)H:flavin oxidoreductase.