PARTIAL-PURIFICATION AND PROPERTIES OF CARMINOMYCIN 4-O-METHYLTRANSFERASE FROM STREPTOMYCES SP STRAIN C5

A methyltransferase that acts on carminomycin and 13-dihydrocarminomyc in, and that is postulated to be the terminal enzyme in the daunomycin biosynthesis pathway, was purified to near-homogeneity from the dauno mycin- and and baumycin-producing Streptomyces sp. strain C5. The enzy me was obtained in approximately 5% yield with a purification of 114-f old in specific activity over the sample precipitated with 30-50% ammo nium sulphate. Polyacrylamide gel electrophoresis under denaturing con ditions indicated a subunit M(r) of about 41000. The enzyme was shown by gel filtration chromatography to have an M(r) of approximately 1660 00, suggesting that it is a homotetramer. Kinetic analysis indicated a n affinity for S-adenosyl-L-methionine typical of antibiotic methyltra nsferases; 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 ana lysis to be daunomycin. The purified enzyme did not catalyse methylati on of the aglycones carminomycinone or 13-dihydrocarminomycinone. S-Ad enosyl-L-homocysteine inhibited the methyltransferase, whereas homocys teine, adenosine, adenine, epsilon-rhodomycinone, daunomycin. and daun omycinone showed little or no inhibitory activity.