This is a family of aromatic ring opening dioxygenases which catalyse the ring-opening reaction of protocatechuate and related compounds [1].

1: Crystal structure of an aromatic ring opening dioxygenase LigAB, a protocatechuate 4,5-dioxygenase, under aerobic conditions. Sugimoto K, Senda T, Aoshima H, Masai E, Fukuda M, Mitsui Y; Structure Fold Des 1999;7:953-965. PMID:10467151