Stizolobate synthase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are L-DOPA and oxygen. Its initial product is 4-(L-alanin-3-yl)-2-hydroxy-cis,cis-muconate 6-semialdehyde.
The intermediate readily cyclises and further oxidises, forming a 2-pyrone ring; this stizolobic acid, which is the product that is isolated and after which this enzyme is named.
The oxidation step uses oxidised nicotinamide adenine dinucleotide as a cofactor and the enzyme also requires zinc. It belongs to the family of oxidoreductases, specifically those acting on single donors with O<sub>2</sub> as oxidant and incorporation of two atoms of oxygen into the substrate (oxygenases). The oxygen incorporated need not be derived from O<sub>2</sub>. The systematic name of this enzyme class is 3,4-dihydroxy-L-phenylalanine:oxygen 4,5-oxidoreductase (recyclizing). It participates in tyrosine metabolism.
A separate enzyme, stizolobinate synthase also present in higher plants cleaves L-DOPA in a way which produces the isomeric compound, stizolobinic acid.