Methylation Pathways in Antibiotic Producing Streptomycetes

摘要: Most secondary metabolites produced in plants and microorganisms contain methyl groups donated from S-adenosylmethionine. While many of these are transferred to oxygen nitrogen atoms, others involve C-methylation form carbon-carbon bonds. Examples pathways which such a reaction occurs include the antibiotics thiostrepton1, indolmycin2, actinomycin3, thienamycin4, anthramycin5, streptonigrin6. The methyltransferases catalyze some reactions have been identified cell-free extracts and, instances, purified homogeneity. Table 1 lists properties several O- N-methyl transferases characterized plant microbial sources 2 summarizes C-methy1trans ferases, including tryptophan C-methy1transferase is topic this paper. It should be noted that all cases studied7,8, mechanism ordered bi-bi type with S-adenosylmethionine binding first its product, S-adenosylhomocysteine, being released last. Also, most studied, group inversion configuration, indicating direct transfer12, but at least two cases, those thienamycin thiostrepton, retention configuration observed, suggesting two—step methylation process1,4. Finally, enzymes inhibited by although KiS often above Km for S-adenosylmethionine, interesting light observed other systems found greater affinity inhibitor than substrate13. However, crude amount S-adenosylhomocysteine present may overestimated unless metabolizing specifically during determination Ki.