A basic glycopeptide antineoplastic antibiotic isolated from Streptomyces verticillus. Bleomycin antibiotics form complexes with iron that react with molecular oxygen to produce superoxide and hydroxyl free radicals, causing single- and double-stranded breaks in DNA. These reactive oxygen species also induce lipid peroxidation, carbohydrate oxidation, and alterations in prostaglandin synthesis and degradation.