Osmium Tetroxide Probes of the DNA Structure. Voltammetric Microanalysis
Osmium tetroxide complexes have been widely used as probes of the DNA structure (1). We showed (2) that osmium tetroxide, pyridine complex (Os,py) covalently bound to pyrimidine bases in denatured single-stranded (ss) DNA was a convenient electroactive marker. Os,py bound to ssDNA was detected with stripping voltammetry at HMDE at concentrations as low as 5 ng/ml (3). Later other ligands (L) such as 2, 2'-bipyridine (bipy) (4) or 1, 1o- phenanthroline (5) were used instead of pyridine providing better stability of the complex. Complex of DNA with Os,bipy (DNA-Os,bipy) produced two types of signals on HMDE (a) three faradaic reversible signals at potentials from 0V to 1 V and (b) a catalytic signal at -1.2 V (against the saturated calomel electrode). The catalytic signal was used for determination of ss regions in supercoiled DNAs (6). Recently conditions have been found under which subnanogram amount of DNA-Os,bipy can be determined by the differential pulse voltammetry. Mercury electrodes were not suitable for studies the DNA - Os, L reaction mixtures without purification due to strong binding of Os, L to the mercury surface. We show that the pyrolytic graphite electrode (PGE) can be applied for this purpose. DNA is adsorbed at PGE, the electrode is washed and the DNA - Os, L adduct determined.
1.E. Palecek, Crit. Rev. Biochem. Mol. Biol. 26, 151-226 (1991).
L. Havran, M. Fojta, M. Tomschik, F. Jelen, E. Palecek
Institute of Biophysics, Academy of Sciences of Czech Republic