ENZYMATIC 12-HYDROXYLATION AND 12-O-METHYLATION OF DIHYDROCHELIRUBINE IN DIHYDROMACARPINE FORMATION BY THALICTRUM-BULGARICUM

Two novel enzymes, dihydrochelirubine-12-hydroxylase and SAM:12-hydroxydihydrochelirubine-12-O-methyltransferase have been discovered in cell-free extracts of yeast-elicited Thalictrum bulgaricum cell cultures. Both enzymes are involved in the last two steps of the biosynthesis of macarpine, the most highly oxidized benzophenanthridine alkaloid found in nature. The hydroxylase is a microsomal-associated, cytochrome P-450-dependent monooxgenase which acts exclusively at C-12 of dihydrochelirubine. The methyltransferase methylates at the expense of SAM highly specifically the hydroxyl moiety at C-12 to form dihydromacarpine. This discovery leads to the complete sequence of macarpine biosynthesis which has thus far been the longest secondary product pathway completely clarified at the enzymic level.