Methods of screening a test agent for activity to modulate an oxidative demethylation enzyme are provided according to embodiments of the present invention which includes preparing a test reaction comprising an oxidative demethylation enzyme, a substrate for the oxidative demethylation enzyme, a test agent and 4-amino-3-penten-2-one under conditions which allow generation of formaldehyde by oxidative demethylation of the substrate by the enzyme in the absence of the test agent; detecting fluorescence in the test reaction, the fluorescence indicative of reaction of formaldehyde and 4-amino-3-penten-2-one in the test reaction; and comparing fluorescence detected in the test reaction with a control, wherein a difference in detected fluorescence is indicative of a change in activity of the oxidative demethylation enzyme in the presence of the test agent.