Part of a two-component P450 system that efficiently O-demethylates diverse aromatic substrates such as guaiacol and a wide variety of lignin-derived monomers. Is likely involved in lignin degradation, allowing Amycolatopsis sp. ATCC 39116 to catabolize plant biomass. GcoA binds and processes the substrate with electrons supplied by the GcoB subunit. guaiacol + O2 + reduced [NADH--hemoprotein reductase] = catechol + formaldehyde + H(+) + H2O + oxidized [NADH--hemoprotein reductase] 3-methoxycatechol + O2 + reduced [NADH--hemoprotein reductase] = 1,2,3-trihydroxybenzene + formaldehyde + H(+) + H2O + oxidized [NADH--hemoprotein reductase] anisole + O2 + reduced [NADH--hemoprotein reductase] = formaldehyde + H(+) + H2O + oxidized [NADH--hemoprotein reductase] + phenol guaethol + O2 + reduced [NADH--hemoprotein reductase] = acetaldehyde + catechol + H(+) + H2O + oxidized [NADH--hemoprotein reductase] 2-methylanisole + O2 + reduced [NADH--hemoprotein reductase] = 2-hydroxytoluene + formaldehyde + H(+) + H2O + oxidized [NADH--hemoprotein reductase] kcat is 6.8 sec(-1) with guaiacol as substrate. kcat is 2.1 sec(-1) with 3-methoxycatechol as substrate. kcat is 3.5 sec(-1) with anisole as substrate. kcat is 1.4 sec(-1) with guaethol as substrate. kcat is 4.6 sec(-1) with 2-methylanisole as substrate. Aromatic compound metabolism. Monomer. Forms a heterodimer with GcoB. Belongs to the cytochrome P450 family.