Subunit B of the Class III extradiol dioxygenase, Protocatechuate 4,5-dioxygenase, which catalyzes the oxidization and subsequent ring-opening of protocatechuate.
Protocatechuate 4,5-dioxygenase (LigAB) catalyzes the oxidization and subsequent ring-opening of protocatechuate (or 3,4-dihydroxybenzoic acid, PCA), an intermediate in the breakdown of lignin and other compounds. Protocatechuate 4,5-dioxygenase is an aromatic ring opening dioxygenase belonging to the class III extradiol enzyme family, a group of enyzmes that cleaves aromatic rings between a hydroxylated carbon and an adjacent non-hydroxylated carbon using a non-heme Fe(II). LigAB is composed of two subunits, designated A and B, which form a tetramer composed of two copies of each subunit. The B subunit (LigB) is the catalytic subunit of LigAB.