314 - Electrochemical oxidation of nucleic acids and proteins at graphite electrode. Qualitative aspects

Abstract

The electrochemical oxidation of DNAs differing in the content of guanine plus cytosine (G+C) was investigated at a pyrolytic graphite electrode by means of differential pulse (DP) voltammetry. At pH 6.4 all samples of DNA studied yielded a peak G on DP voltammograms corresponding to the oxidation of the guanine residues, and a peak A corresponding to the oxidation of the adenine residues. The potentials of the peaks G and A were not influenced by the G+C content in DNA and differed by 0.28 V. It was found that the ratio of the heights of the peaks A and G was identical with great accuracy to the ratio of the contents (adenine+thymine) and (G+C). This fact was exploited for developing a new method for the determination of the G+C content in DNA. The electrochemical oxidation of proteins at a spectroscopic graphite electrode impregnated with paraffin wax (WISGE) was studied by means of linear sweep, cyclic, and DP voltammetry. It was found that proteins were electrochemically oxidizable at the WISGE. They yielded a faradaic peak on voltammograms in the vicinity of 0.7–0.8 V in a neutral medium. The voltammetric study of proteins, poly-(aminoacids), peptides of known aminoacid composition and free aminoacids revealed that the irreversible electrooxidation of tyrosine (and, contingently, of tryptophan) residues is responsible for the appearance of the protein peak at the WISGE. It is suggested that DP voltammetry at a graphite electrode might become another electrochemical method suitable for studies of conformational changes of proteins, and in particular of those not containing cystine or cysteine ( e.g. histones).