Biosynthesis of anthracyclines: carminomycin 4-O-methyltransferase, the terminal enzymic step in the formation of daunomycin

In the presence of S-adenosyl-l-methionine, cell-free extracts of Streptomyces sp. C5, Streptomyces peucetius ATCC 29050, Streptomyces insignis ATCC 31913 and Streptomyces coeruleorubidus ATCC 31276 O-methylated carminomycin and 13-dihydrocarminomycin to daunomycin and 13-dihydrodaunomycin, respectively. With the corresponding aglycones, carminomycinone and 13-dihydrocarminomycinone, as substrates, no methylated products were detected. Other 4-hydroxyanthracyclines such as aklavin and aclacinomycin A, and 4-hydroxyanthracyclinones such as ɛ-rhodomycinone and aklavinone, were not substrates for the 4-O-methyltransferase. These reaction specificities indicate that glycosylation of the anthracyclinone molecule must occur before 4-O-methylation, which means that 4-O-methylation of carminomycin is probably the terminal step in the biosynthesis of daunomycin, and that daunomycinone is not an intermediate in the pathway.