[7] Measurement of iron and copper in biological systems: Bleomycin and copper-phenanthroline assays

This chapter discusses the measurement of iron and copper in biological systems. It focuses on bleomycin and copper-phenanthroline assays. Bleomycin is an antitumor antibiotic produced by fermentation of Streptomyces verticillus. Clinical preparations of bleomycin are active against several human cancers including Hodgkin's disease and cancer of the testes. Bleomycins are a family of glycopeptide antibiotics, which are able to chelate metal ions through their secondary amide groups. The clinical effects are thought to be because of binding of bleomycin to DNA adjacent to guanosine residues, where it interferes with helix unwinding, replication, and transcription and may cause both single- and double-strand breakages. Additionally, degradation of deoxyribose occurs, forming several products among, which are base propenals that further break down to release the three-carbon aldehyde malondialdehyde. The chelating agent 1,10-phenanthroline degrades DNA in the presence of copper ions, O2, and a suitable reducing agent by a mechanism known to involve oxygen radicals, probably •OH. As in bleomycin-mediated DNA degradation, the deoxyribose moieties of the DNA are attacked, resulting in the formation of malondialdehyde that may be quantitated in the thiobarbituric acid (TBA) test.