REACTIONS OF GLYOXAL WITH NUCLEIC ACIDS NUCLEOTIDES AND THEIR COMPONENT BASES

The reactions of glyoxal with nucleic acids, nucleotides and their bases were examined by measuring spectral changes. The spectra of all of the bases and nucleotides in RNA and DNA were changed appreciably by treatment with a high concentration of glyoxal. When treated with a low concentration of glyoxal, however, only guanine or guanylic acid underwent a specific spectral change. The reaction of glyoxal with this base or its nucleotide proceeded to completion within 30 min between pH 8.3 and 9.8 as estimated from the spectral change at room temperature. This phenomenon was applied for determination of the guanosine content of nucleic acids and the results agreed well with previous data obtained by chromatography. As judged from the spectral change, glyoxal did not react with native calf thymus DNA, while it reacted considerably with heat-denatured DNA. The spectral change obtained with denatured DNA was a composite of two qualitatively different changes, the change being due solely to the reaction between glyoxal and guanosine residues and the hyperchromic shift of the 260-mμ band, which may be a secondary effect of the reaction. From the analysis of these two effects, the degree of reaction of the guanosine residues in denatured DNA was estimated to be 72 %. © 1968.