Norcoclaurine synthases with increased acitvity

A method for preparing a composition of matter comprising a benzylisoquinoline alkaloid (BIA) from a (S)-norcoclaurine and/or (S)-norlaudanosoline substrate comprising the steps of:

• a) providing a recombinant host cell comprising a variant norcoclaurine synthase capable of catalyzing the condensation of 4-hydroxy-phenylacetaldehyde (4-HPAA) and dopamine into (S)-norcoclaurine and/or 3,4-dihydroxy-acetaldehyde (3,4-DhPAA) and dopamine into (S)-norlaudanosoline, wherein the variant norcoclaurine synthase comprises:
• i) one or more site-specific substitutions corresponding to positions 73, 77, 99, 114, 142, 152, 174, and 178 of SEQ ID NO:
• 1;
• or
• ii) one or more site-specific substitutions corresponding to positions 73, 77, 99, 114, 142, 152, 174, and/or 178 of SEQ ID NO:
• 1, and an N-terminal truncation;
• and
• b) culturing the recombinant host cell under conditions promoting said catalyzation;
• and optionally
• c) isolating the BIA.