Spectroscopic studies of STZ-induced methylated-DNA in both in vivo and in vitro conditions.

Alkylating agents after formation of DNA adduct not only possess their harmful role on living cells but also can transfer this information to the next generation. Different techniques have been introduced to study the alkylated DNA, most of which are specific and designed for investigation of specific target DNA. But the exact differences between spectroscopic and functional properties of alkylated DNA are not seen in the literature. In the present study DNA was methylated using streptozotocin (STZ) by both in vitro and in vivo protocols, then methylated-DNA was investigated by various techniques. Our results show that (1) the binding of ethidium bromide as an intercalating dye decreases to methylated-DNA in comparison with normal DNA, (2) CD spectra of methylated-DNA show changes including a decrease in the positive band at 275 nm and a shift from 258 nm crossover to a longer wavelength, which is caused by reduction of water around it, due to the presence of additional hydrophobic methyl groups, (3) the stability of methylated-DNA against DTAB as a denaturant is decreased and (4) the enzyme-like activity of methylated-DNA in an electron transfer reaction is reduced. In conclusion, additional methyl groups not only protrude water around DNA, but also cause the loss of hydrogen bonding, loosening of conformation, preventing desired interactions and thus normal function of DNA.