Oxygenases are a class of proteins which catalyze the incorporation of one atom of oxygen into the substrate molecule. The oxygen atom incorporateci into the substrate is exclusively derived from molecular oxygen (for an overview, see Reference 1). This was unambiguously proven by using 18 02 as a cosubstiate.
van Berkel, W. J. H., & Müller, F. (1991). Flavin-dependent monooxygenases with special reference to p-hydroxybenzoate hydroxylase. In F. Muller (Ed.), Chemistry and biochemistry of flavoenzymes (1st ed., Vol. 2, pp. 1-29). CRC Press. https://doi.org/10.1201/9781351070584-1