Apparent low-field microwave absorption in Escherichia coli endonuclease III: A possible way for increased DNA damage by the microwave effect

We observe an anomalous low-field microwave absorption for Escherichia coli endonuclease III in the process of measuring the electron magnetic resonance. To understand this, we firstly paid attention to a three-dimensional structure of the [4Fe-4S] cubane cluster existing in endonuclease III and then built fluctuating electric dipoles driven by both mixed-valence characteristics of a [4Fe-4S] cluster and its double exchange mechanism between Fe²⁺ and Fe³⁺. By using this model, we were able to explain the microwave absorption in terms of electric dipole transitions between excited states of the [4Fe-4S] cluster. Finally, a possible effect of this microwave absorption on a repair rate of the damaged-DNA is discussed.