Partial purification and properties of carminomycin 4-O-methyltransferase from Streptomyces sp. strain C5

A methyltransferase that acts on carminomycin and 13-dihydrocarminomycin, and that is postulated to be the terminal enzyme in the daunomycin biosynthesis pathway, was purified to near-homogeneity from the daunomycin- and baumycin-producing Streptomyces sp. strain C5. The enzyme was obtained in approximately 5% yield with a purification of 114-fold in specific activity over the sample precipitated with 30-50% ammonium sulphate. Polyacrylamide gel electrophoresis under denaturing conditions indicated a subunit M(r) of about 41,000. The enzyme was shown by gel filtration chromatography to have an M(r) of approximately 166,000, suggesting that it is a homotetramer. Kinetic analysis indicated an affinity for S-adenosyl-L-methionine typical of antibiotic methyltransferases; the enzyme had a slightly higher affinity for carminomycin than for 13-dihydrocarminomycin. The reaction product from methylation of carminomycin was confirmed by chromatography and mass spectral analysis to be daunomycin. The purified enzyme did not catalyse methylation of the aglycones carminomycinone or 13-dihydrocarminomycinone. S-Adenosyl-L-homocysteine inhibited the methyltransferase, whereas homocysteine, adenosine, adenine, epsilon-rhodomycinone, daunomycin, and daunomycinone showed little or no inhibitory activity.