Plasmid and chromosomal DNA of E. coli during exponential growth are cleaved after treatment with copper(II)-1, 10-phenanthroline complex (1: 2) without providing any exogenous reductant. About 1500 copper molecules per cell are present as estimated by atomic absorption analysis. Within the cell the endogenous reducing substances may have participated in the sequential oxidative reactions, which lead to the damage of DNA. A portion of the resultant DNA fragments originates from plasmid DNA as demonstrated by hybridization tests.
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