The enzyme, characterized from the bacterium Pseudomonas alcaligenes NCIMB 9867, catalyses the hydrolysis of 3-maleylpyruvate, the ring-cleavage product of gentisate. The enzyme can also act on a number of maleylpyruvate derivatives, such as (2E)-2-methyl-4,6-dioxohept-2-enedioate and (2E)-3-methyl-4,6-dioxohept-2-enedioate. Activated by Mn2+. May be identical to EC 3.7.1.5, acylpyruvate hydrolase.