In enzymology, a stizolobinate synthase (EC 1.13.11.30) is an enzyme that catalyzes the chemical reaction

3,4-dihydroxy-L-phenylalanine + O₂ ${\displaystyle \rightleftharpoons }$ 5-(L-alanin-3-yl)-2-hydroxy-cis,cis-muconate 6-semialdehyde

Thus, the two substrates of this enzyme are 3,4-dihydroxy-L-phenylalanine and O₂, whereas its product is 5-(L-alanin-3-yl)-2-hydroxy-cis,cis-muconate 6-semialdehyde.

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 3,4-dihydroxy-L-phenylalanine:oxygen 2,3-oxidoreductase (recyclizing). This enzyme participates in tyrosine metabolism. It employs one cofactor, zinc.