In enzymology, a stizolobate synthase (EC 1.13.11.29) is an enzyme that catalyzes the chemical reaction

3,4-dihydroxy-L-phenylalanine + O₂ ${\displaystyle \rightleftharpoons }$ 4-(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 4-(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 4,5-oxidoreductase (recyclizing). This enzyme participates in tyrosine metabolism. It employs one cofactor, zinc.

• Saito K, Komamine A (1976). "Biosynthesis of stizolobinic acid and stizolobic acid in higher plants. An enzyme system(s) catalyzing the conversion of dihydroxyphenylalanine into stizolobinic acid and stizolobic acid from etiolated seedlings of Stizolobium hassjoo". Eur. J. Biochem. 68 (1): 237–43. doi:10.1111/j.1432-1033.1976.tb10783.x. PMID 9285.
• Saito K, Komamine A (1978). "Biosynthesis of stizolobinic acid and stizolobic acid in higher plants". Eur. J. Biochem. 82 (2): 385–92. doi:10.1111/j.1432-1033.1978.tb12033.x. PMID 624278.