Cytochrome P450BM3-F87G catalyzed the oxidative defluorination of 4-fluorophenol, followed by reduction of the resulting benzoquinone to hydroquinone via the NADPH P450-reductase activity of the enzyme. The k catand K m for this reaction were 71 ± 5 min-1 and 9.5 ± 1.3 mM, respectively. Co-incubation of the reaction mixture with long chain aldehydes stimulated the defluorination reaction, with the 2,3-unsaturated aldehyde, 2-decenal producing a 12-fold increase in catalytic efficiency. At 150 µM aldehyde, k cat increased to 158 ± 4, while K m decreased to 1.8 ± 0.2. The effects of catalase, glutathione and ascorbate on the reaction were all consistent with a direct oxygen insertion mechanism, as opposed to a radical mechanism. The study demonstrates the potential use of P450BM3 mutants in oxidative defluorination reactions, and characterizes the novel stimulatory action of straight chain aldehydes on this activity.