Involved in the biosynthesis of the anthracycline aclacinomycin which is an aromatic polyketide antibiotic that exhibits high cytotoxicity and is widely applied in the chemotherapy of a variety of cancers. In vivo and in vitro, RdmB catalyzes the removal of the carboxylic group from the C-10 position of 15-demethoxyaclacinomycin T coupled to hydroxylation at the same C-10 position. It could also catalyze the removal of the carboxylic group at the C-10 position of 15-demethoxy-epsilon-rhodomycin coupled to hydroxylation at the same C-10 position to yield rhodomycin B. The reaction catalyzes by RdmB is intriguing, since the enzyme does not use any of the cofactors usually associated with hydroxylases such as flavins and/or metal ions to activate molecular oxygen. 15-demethylaclacinomycin T + AH2 + O2 = 10-decarboxymethylaclacinomycin T + A + CO2 + H2O Inhibited by sinefungin and S-adenosyl-L-homocysteine. Antibiotic biosynthesis; aclacinomycin biosynthesis. Antibiotic biosynthesis; rhodomycin biosynthesis. Homodimer and homotetramer in equilibrium. Although RdmB shows significant similarity to methyltransferase family, it cannot act as a methyltransferase. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family.