The influence of pH on the inhibition of DNA cleavages induced by pyrogallol.

Induction of DNA damage by pyrogallol has been shown at physiological pH, but mutagenesis data also suggest there is inhibition in acidic media. In the present work, the plasmid pBSK was incubated with pyrogallol, under aerobic conditions at 37 degrees C, at pH 7.4, 4.5 or 3.5, for 1, 3 or 5 h, in the absence or presence of Cu(2+). Cleavage of the supercoiled DNA form was analyzed through topology modifications by agarose gel electrophoresis and quantified by densitometry. Independently of the presence of Cu(2+), DNA cleavage at pH 7.4 was significantly (P < 0.001) induced and occurred extensively after 1-h incubation. At pH 4.5, the cleavage was significantly (P < 0.05) induced only after 5 h incubation in the absence of Cu(2+), but was extensive (P < 0.001) after 1-h incubation when the metal ion was present. At pH 3.5, DNA cleavage was inhibited (P > 0.05), after 5-h incubation, even in the presence of Cu(2+). Our results provide evidence that DNA cleavage by pyrogallol is pH-dependent, catalyzed by Cu(2+) , and extensively decreased in acidic pH. Due to the abundant presence of the pyrogallate ion in physiological media, we suggest that this conjugate base form is responsible for DNA cleavage.