Involved in the last but one step of the biosynthesis of berberine, an antimicrobial benzylisoquinoline alkaloid. Converts (S)-tetrahydrocolumbamine (THC) to (S)-tetrahydroberberine (THB) also called (S)-canadine. (S)-tetrahydrocolumbamine + O2 + reduced [NADPH--hemoprotein reductase] = (S)-canadine + H(+) + 2 H2O + oxidized [NADPH--hemoprotein reductase] Expressed at low levels in roots. Belongs to the cytochrome P450 family.