Figure 3: Light-induced activation of complex 1 induces DNA single strand breaks (DNA nicks) in plasmid DNA and is inhibited by addition of ethidium bromide or in hypoxic conditions.

(A) Electrophoresis of PUC19 plasmid DNA treated with (+) and without (−) 405 nm light (3.6 J cm⁻²) and between 0 μM and 1 μM of complex 1. 0.3 μg DNA was loaded from each sample. Lanes 1–3 represent control DNAs where nicks/single strand breaks were induced by rapid freeze thawing of DNA and linearization induced using a restriction endonuclease. (B) Quantification of the light-induced change in ratio of nicked to supercoiled DNA. Values represent fold increase in ratios in light exposed compared to non-exposed samples. (C) Quantification of the light-induced change in ratio of nicked to supercoiled DNA when ethidium bromide (EtBr) was included in the reaction. (D) Quantification of the light-induced change in ratio of nicked to supercoiled DNA when reactions were carried out under normoxic or under hypoxic (0.1% oxygen) conditions. Data shown are mean and standard deviation of at least 3 independent experiments. Significance was determined using the Student’s T-test where n = 3 and p < 0.05 is indicated by ^*.