[Investigation of alkylation in rat liver chromatin after application of 3H-cyclophosphamid--"fine-distribution" and kinetics].

The alkylation of chromatin constituents (DNA, histones and non-histones) in liver cell nuclei was investigated at various times after intraperitoneal injection of rats with 3H-cyclophosphamid. The highest alkylation was found in the DNA, the lowest in the histones; the euchromatic portions were alkylated several times higher compared to those of the heterochromatin. The eventual elimination of 3H-activity with time indicates that cyclophosphamid leads to repair processes in the DNA, this conclusion being supported by other experimental observations. In some of the 16 subfractions of the nonhistone proteins, alkylated portions are apparantly eliminated by normal protein turnover; however, in other nonhistones this elimination is inhibited, whereby in one subfraction it seems to be accelerated. The results of analog experiments with 14C-tryptophan as a precursor for nonhistone protein synthesis serve as a reference for this. In supplementary in-vitro model experiments using triaziquon as an alkylating agent indications for DNA-Protein-cross-links in chromatin could be obtained by the technique of X-ray low angle scattering, and according to sedimentation behaviour.