Figure 6.

Enzymes functioning in reticuline metabolism. The biogenesis of (S)-reticuline begins with (L)-tyrosine. While a number of subsequent intermediates are made through different pathways, they converge on the production of (S)-noroclaurine via the enzymatic activity of noroclaurine synthase (E.C. 4.2.1.78). Subsequent enzymatic steps include norcoclaurine 6-O-methyltransferase (E.C. 2.1.1.128), coclaurine N-methyltransferase (E.C. 2.1.1.140), the CYP80B1 N-methylcoclaurine 3′-monooxygenase (E.C. 1.14.13.71), 3′-hydroxy-N-methylcoclaurine 4′-O-methyltransferase (E.C. 2.1.1.116), berberine bridge enzyme tetrahydroprotoberberine synthase (reticuline oxidase) (EC 1.5.3.9). (S)-reticuline is an intermediate whose subsequent metabolism results in the generation of a wide number of isoquinoline alkaloids that are an important response to pathogen attack. Supplemental data is provided (Table S2).^229-237