2-STEP EPOXIDATION OF HYOSCYAMINE TO SCOPOLAMINE IS CATALYZED BY BIFUNCTIONAL HYOSCYAMINE 6-BETA-HYDROXYLASE

In several solanaceous plants, hyoscyamine is first hydroxylated at th e 6beta-position, and then epoxidized to scopolamine. We expressed hyo scyamine 6beta-hydroxylase (H6H) in Escherichia coli as a fusion prote in with maltose-binding protein. The crude cell extract from the bacte rium that expressed the soluble fusion protein showed a strong hydroxy lase activity and a weak epoxidase activity. When 100 muM of hyoscyami ne was fed to the recombinant bacterium, the alkaloid was first conver ted to 6beta-hydroxyhyoscyamine, and then to scopolamine, which was al most the only alkaloid found in the culture after one week. Therefore, H6H catalyzes two consecutive reactions that oxidize hyoscyamine to s copolamine.