Summary: Aklanonic acid, a substituted anthraquinone, is the earliest stable intermediate isolated so far in the biosynthesis of anthracycline antibiotics. Desalted, soluble cell extracts of sp. C5 and (ATCC 29050) converted aklanonic acid to ɛ-rhodomycinone in an -adenosyl-L-methionine- and NADPH-dependent sequence of reactions. Aklanonic acid was methylated to form aklanonic acid methyl ester (AAME), which was cyclized to form aklaviketone. Aklaviketone was reduced to aklavinone by an NADPH-linked reductase. When extracts of sp. C5 and were used, aklavinone was hydroxylated at C-11 by an NADPH- and oxygen-dependent reaction to form ɛ-rhodomycinone. Cell extracts of strains ATCC 31133 and 31671 converted aklanonic acid to aklavinone in the same manner, but neither of the strains hydroxylated aklavinone to ɛ-rhodomycinone. Mutants of sp. C5 blocked at steps in the conversion of aklanonic acid to aklavinone, and which accumulated aklanonic acid (SC5-39; ), AAME (SC5-138; ), and aklaviketone (SC5-159; ), lacked the expected enzymic activities. In a mutant (SC5-24; ) lacking aklaviketone reductase, but retaining aklavinone 11-hydroxylase activity, maggiemycin was formed as an apparent shunt product. An enzymic pathway for ɛ-rhodomycinone and maggiemycin formation is consistent with the data presented.


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