Significance NOV1 is a stilbene cleavage oxygenase (SCO). SCOs cleave the central double bond of stilbenes, forming two phenolic aldehydes. Many stilbenes, such as resveratrol, are produced by plants as secondary metabolites. They are also formed from lignin during kraft pulping. SCOs are related to carotenoid cleavage oxygenases (CCOs), which cleave β-carotene or apocarotenoids. Carotenoids play important roles in photosynthesis and light perception in the eye. We present the structure of an SCO and the structure of a CCO-related enzyme in ternary complex with oxygen and substrate. This structure allows us to propose a mechanism relevant to both SCOs and CCOs, where the substrate is activated for reaction with a ferric-superoxo electrophile by active site base-catalyzed deprotonation of a phenol group.