Involved in the modified meta-cleavage pathway for the 2-aminophenol catabolism. (S)-4-hydroxy-2-oxopentanoate = (2Z)-2-hydroxypenta-2,4-dienoate + H2O Strongly inhibited by Fe(2+), Fe(3+), K(3)[Fe(CN)(6)], Ag(+), and Cu(2+). Optimum pH is 7.5. Stable in the range of pH 5.0-8.0. Stable up to 35 degrees Celsius. Forms a complex with AmnE. Belongs to the hydratase/decarboxylase family.