Temperature-dependent formation of a conjugate between Tris(hydroxymethyl)aminomethane buffer and the malondialdehyde-DNA adduct pyrimidopurinone

The stability of the major adduct formed between the endogenous product malondialdehyde (MDA) and deoxyguanosine, a pyrimidopurinone termed M₁G-dR, was tested under a variety of conditions required for nucleic acid manipulation. M₁G-dR was found to be stable at neutral pH and 37°C but to be unstable when stored at -20 °C in the presence of Tris buffers. A new product with a characteristic absorption band at 350 nm was identified by ¹H-NMR as an enamino-imine comprised of one molecule of Tris, one molecule of MDA, and deoxyguanosine. The formation of the conjugate was observed on reaction of Tris with M₁G-dR or its ring-opened derivative N²-(3-oxo-1- propenyl)deoxyguanosine. The Tris-M₁G-dR conjugate was unstable in aqueous solutions at room temperature, undergoing hydrolysis. However, the Tris conjugate of M₁G base remained stable at room temperature in organic solvent. The isolation and properties of a conjugate between M₁G-dR and Tris suggest that cross-links may form by reaction of MDA with DNA but they are likely to be unstable to hydrolysis.