Alkylated DNA: Buoyant density changes and modes of decomposition

Abstract

1. 1. Alkylation of DNA with nitrogen mustard ( N-methyl-bis(2-chloroethyl)-amine·HCl) causes a reduction in buoyant density. The magnitude of the effect depends on the amount of 14C-labeled nitrogen mustard bound and is independent of the DNA base composition. 2. 2. The relative hypodensities in CsCl, CsCl-LiCl (2:1 mole ratio), and Cs 2SO 4 were measured. A method for the analysis of this type of data is proposed. It was concluded that the buoyant density reduction is mainly due to a large increase in hydration, the extent of which was estimated. 3. 3. The increased hydration may be due to the presence of an ammonium ion on the bound nitrogen mustard moiety. The effect of pH on the hypodensity of nitrogen mustard reacted DNA supported this supposition. 4. 4. When nitrogen mustard reacted DNA is heated, the hypodensity is gradually lost concomitantly with a loss of bound 14C-labeled nitrogen mustard. In addition, the DNA breaks down to lower molecular weight fragments. The two modes of decomposition have different pH-dependences. The results, nevertheless, did not exclude a hypothetical two step decomposition process involving elimination of alkylguanine followed by strand scission.