Polarographic reducibility of denatured DNA

The de polarographic behavior of native and denatured DNA at pH 7.0 was studied. Whereas native DNA was polarographically inactive under the given conditions, denatured DNA yielded a reduction polarographic step at the potential of about ?1.4 V. Native DNA produced a single desorption wave on ac polarograms, while denatured DNA yielded, in addition to this wave, another more negative wave approximately corresponding, as to its potential, to the dc polarographic step of denatured DNA. The behavior of apurinic acid was similar to that of denatured DNA. The course of DNA denaturation at elevated temperature was studied by means of the two above techniques and changes at temperatures below the melting temperature observed. This finding is in agreement with earlier results obtained by oscillopolarographic and the pulse-polarographic method.     

Renaturation of denatured DNA in NaI gradients

We show that denatured DNA from Tetrahymena mitochondria or phage T₇, partially renatures during centrifugation in NaI equilibrium density gradients. This makes these gradients unsuitable for the analysis of single-stranded complementary nucleic acids, especially if their complexity and mole percent G+C are low.