In enzymology, berbamunine synthase (, Formerly and ) is an enzyme that catalyzes the combination of two benzylisoquinoline alkaloids
The enzyme has a cofactor, a reduced nicotinamide adenine dinucleotide phosphate in combination with a hemoprotein, which allows it to use molecular oxygen to oxidatively combine the alkaloid substrates.
It can combine related alkaloids differing only in the degree of methylation of the phenolic oxygens. For example, (S)-coclaurine also reacts with (R)-N-methylcoclaurine to give 2'-norberbamunine and dimerisation of (R)-N-methylcoclaurine gives guattegaumerine.
The enzyme belongs to the family of oxidoreductases and its systematic name is (S)-N-methylcoclaurine,NADPH:oxygen oxidoreductase (C-O phenol-coupling). It is also called (S)-N-methylcoclaurine oxidase (C-O phenol-coupling). It was first isolated from Berberis stolonifera and participates in alkaloid biosynthesis.