Nucleic-acid binding by tetracycline·metal ion complexes

Tetracycline forms chelate complexes with cupric, nickelous, and cobaltous ions that bind DNA when analyzed in a filter-retention assay. Tetracycline complexes with other metal ions including zinc, ferrous, ferric, manganous, magnesium, and calcium ions do not produce this effect. The tetracycline·copper complex binds the homopolymers polyriboadenylate, polyribouridylate, polyriboinosinate, and polyribocytidylate. The binding of polyribocytidylate is least effective. The preaddition of calcium ions interferes with the ability of tetracycline to form a DNA-binding complex with cupric ions. Calcium ions do not block DNA binding by an already formed tetracycline·copper complex.

Riboflavin interferes with the DNA-binding action of tetracycline in the filter-retention assay. This suggests a rationale for its reported antagonism of bacterial growth inhibition by tetracycline. Riboflavin does not block the DNA-binding activity of an already formed tetracycline·copper complex. None of the riboflavin·metal ion complexes tested are capable of binding DNA in the filter-retention assay.