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). LigXd probably transfers the electrons from NADH to LigXc. 5,5'-dehydrodivanillate + H(+) + NADH + O2 = 2,2',3-trihydroxy-3'-methoxy-5,5'-dicarboxybiphenyl + formaldehyde + H2O + NAD(+) Binds 1 FAD per monomer. kcat is 538 sec(-1) with NADH as substrate. Optimum pH is 6.0. Optimum temperature is 25-30 degrees Celsius. Monomer. The three-component monooxygenase is composed of an oxygenase (LigXa), a ferredoxin (LigXc) and a ferredoxin reductase (LigXd). Disruption mutant shows growth defect on DDVA. Belongs to the FAD-dependent oxidoreductase family.