In enzymology, a peptide-tryptophan 2,3-dioxygenase (EC 1.13.11.26) is an enzyme that catalyzes the chemical reaction

peptide tryptophan + O₂ ${\displaystyle \rightleftharpoons }$ peptide formylkynurenine

Thus, the two substrates of this enzyme are peptide tryptophan and O₂, whereas its product is peptide formylkynurenine.

This enzyme belongs to the family of oxidoreductases, specifically those acting on single donors with O₂ as oxidant and incorporation of two atoms of oxygen into the substrate (oxygenases). The oxygen incorporated need not be derived from O₂. The systematic name of this enzyme class is peptide-tryptophan:oxygen 2,3-oxidoreductase (decyclizing). Other names in common use include pyrrolooxygenase, peptidyltryptophan 2,3-dioxygenase, and tryptophan pyrrolooxygenase.