Iron(II) induces changes in the conformation of mammalian mitochondrial DNA resulting in a reduction of its transcriptional rate.

Living isolated mitochondria incubated with iron(II) show a major alteration in mitochondrial DNA (mtDNA) conformational forms as assessed by Southern blot analysis of undigested mtDNA. In the presence of iron(II), form I is transformed into form III in a dose-dependent manner. This alteration in mtDNA conformation shows a strong correlation with a decrease in the mtDNA transcription rate (r=0.965, P < 0.002), suggesting that iron(II) load results in double-strand breaks and unwinding of mtDNA, which, in turn, is unable to maintain its normal transcriptional rate.