DNA Cleavage by Good’s Buffers in the Presence of Au(III)

Abstract

Abstract DNA (pBluescript plasmid, 2.96 kbp) cleavage by Good’s buffers, which are extensively used in laboratories of chemistry, biochemistry, or biology, was studied by gel electrophoresis, CD spectra, ESR spectra, and CV in the presence of Au(III). Incubation of plasmid DNA with Good’s buffers and Au(III) resulted in DNA cleavage. DNA cleavage occurred due to the formation of nitrogen-centered cationic free radicals from the Good’s buffers in the presence of Au(III). The formation of the nitrogen-centered free radicals was confirmed by ESR spectroscopy. Gel electrophoresis results indicated that Form I and Form II were converted into Form III and a DNA fragment. The molecular weight of the DNA fragment was estimated ca. 1.47 kbp by DNA marker gel electrophoresis. ESR spectra were not observed from the Good’s buffers in the presence of other metal ions, such as Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Pd(II), Cd(II), Hg(II), and Pb(II), resulting in no DNA cleavage. Gel electrophoresis results indicated a partial DNA cleavage during the incubation of DNA in the presence of Good’s buffers and Au(III). This is because the DNA cleavage reaction stopped at 15 min, since the radical lifetime is ca. 15 min. The intensities of the CD spectra at 270 nm decreased with time by 15 min upon the addition of Au(III), and a constant CD spectrum was observed after 15 min. Further addition of Au(III) showed an alternation of the CD spectra from positive ellipticity to negative ellipticity at 270 nm, suggesting significant DNA cleavage. The mechanism of DNA cleavage is discussed based on the gel electrophoresis, ESR, CD, and CV results.