Abstract: The invention relates to norcoclaurine synthases and substrate binding sites having one or more site-specific mutation which increase the activity, when compared to the wild type synthase, of the condensation of 4-HPAA and dopamine to (S)-norcoclaurine and/or 3,4-DhPAA and dopamine to (S)-norlaudanosoline. The inventors both identified specific mutations corresponding to at position 73, 75, 77, 82, 99, 114, 141, 142, 147, 152, 174 and/or 178 in the count according to SEQ ID No: 1, and sites corresponding to the binding domains defined in SEQ ID NO: 4 and 5, where the mutated increase of the activity may be positioned within these norcoclaurine synthases. These domains are conserved regions.

Abstract: Recombinant microorganisms, plants, and plant cells are disclosed that have been engineered to have reduced levels or activity of one or more alcohol dehydrogenases or aldehyde reductases thereby increasing the production of benzylisoquinoline alkaloids and/or benzylisoquinoline alkaloid precursors.