EPR study on the interaction of spin-labelled hydrazine mustard derivatives with DNA

The interaction of three spin-labelled compounds, derivatives of bis-(2-chloroethyl)-hydrazine (HMSL), N-methyl,N-chloroethyl-hydrazine (MCEHSL) and bis-(2-bromoethyl)-hydrazine (BEHSL) with DNA was studied by the method of electron paramagnetic resonance (EPR). It was found that HMSL (containing two chloroethyl groups) and MCEHSL (containing one chloroethyl group) gave spin-labelled dsDNA with identical strongly immobilized EPR spectra. The conclusion was drawn that only one of the alkylating groups of HMSL reacted with DNA. In contrast, the EPR spectrum of DNA spin-labelled with BEHSL was non-immobilized due to the strong destabilizing effect of this compound on the double helix. The extent of alkylation of DNA with the three hydrazine mustard derivatives was one and the same. It was found, however, that chloroethyl-containing derivatives (HMSL and MCEHSL) had an expressed base specificity and alkylated preferably the guanilic residues, and their bromo-analogue (BEHSL) did not show any base specificity and alkylated the bases of DNA at random.