Involved in the catabolism of 5,5'-dehydrodivanillate (DDVA), an intermediate in the biodegradation of lignin. Part of a three-component monooxygenase that catalyzes the O-demethylation of DDVA, leading to the formation of 2,2',3-trihydroxy-3'-methoxy-5,5'-dicarboxybiphenyl (OH-DDVA). 5,5'-dehydrodivanillate + H(+) + NADH + O2 = 2,2',3-trihydroxy-3'-methoxy-5,5'-dicarboxybiphenyl + formaldehyde + H2O + NAD(+) Binds 1 [2Fe-2S] cluster per subunit. Binds 1 Fe cation. Optimum pH is 6.0. Optimum temperature is 25-30 degrees Celsius. Homotrimer. The three-component monooxygenase is composed of an oxygenase (LigXa), a ferredoxin (LigXc) and a ferredoxin reductase (LigXd). Mutant can degrade syringate and vanillate, but not DDVA. It lacks DDVA O demethylation activity (PubMed:10788391). It cannot grow on minimal medium containing DDVA (PubMed:25217011). Belongs to the bacterial ring-hydroxylating dioxygenase alpha subunit family.