The intra-chromosomal distribution of ( 3 H)-dimethylaminoazobenzene in rat liver nuclei in vivo

[Interaction of p-Dimethylaminoazobenzene with rat liver-chromatin and non-histones (author's transl)]

The carcinogenic p-Dimethylaminoazobenzene and the non-carcinogenic p-aminoazobenzene were radioactive labelled and applicated to Whistar rats intraperitoneally. A very significant difference in binding tendencies for the two compounds and their metabolites was observed in rat liver tissues, rat liver nuclei and rat liver chromatin. Above all a specific binding affinity of the carcinogen to nuclear non-histone protein was found.

Changes in liver nuclear protein metabolism after a single dose of urethane to suckling mice

Treatment of 8-9-day-old C57BL/A mice with a single carcinogenic dose of urethane, at 1.2 mg/g body wt., resulted in an immediate decrease in liver DNA synthesis reaching a maximum at about 16-18 h after injection, the rate of synthesis returning to normal after 48 h. When the nuclear proteins were radiolabelled, the non-histone protein (NHP) fraction showed a significant decrease in specific activity 8-18 h after injection of urethane and slight increase in specific activity after 24 h. Histone and residual proteins did not show any significant change. The liver NHP were analysed by isoelectric focusing (IEF) and sodium dodecyl sulphate (SDS) electrophoresis in polyacrylamide gels. The latter technique failed to show any distinctive differences but IEF results indicated some quantitative and qualitative changes in protein content and synthesis were induced by the urethane treatment. The most noticeable change in the stained gels was an increase in a protein component having a pI of 7.35 and the appearance of new bands at pI's of 7.85 and 5.55 in the 18 h treated livers. However, the [3H]tryptophan labelling pattern indicated that this was not due to an increased synthesis of these components. 24 h after urethane there appeared to be an increased rate of synthesis of some of the major components of the mixture, particularly at the pI 5.65 region. Histone and residual protein fractions were also analysed by electrophoresis and showed no difference between treated and control livers.

In vitro acylation of the xi-amino group of L-lysine in calf thymus histones by the carcinogen, beta-propiolactone

We had previously reported that the carcinogen, beta-propiolactone (BPL) reacted in vitro with histones in whole mouse skin chromatin and that among the histone classes BPL was preferentially bound to the lysine-rich histones H1 and H1 degrees. In order to determine if in vitro reaction of BPL with calf thymus histones resulted in binding of BPL to L-lysine, we synthesized the model compounds XI-N-(3-hydroxypropionyl)lysine (HPL) and xi-N-(I-carboxyethyl)lysine (CEL) from BPL and L-lysine. The alpha-amino group of L-lysine was protected from reaction with BPL by the formation of a copper chelate. Structures were assigned on the basis of infrared spectra, pKa values and chemical analyses. BPL was reacted in vitro with calf thymus histones and the BPL-reacted calf thymus histones and control calf thymus histones were digested with trypsin followed by pronase. The respective digests were each chromatograhed on a column of AA-15 cation-exchange resin. The elution profiles of the two digests were very similar except for the appearance of a new ninhydrin-positive peak (NNPP) in the eluate of the trypsin-pronase digest of BPL-reacted calf thymus histones. When compounds HPL and CEL were added to the trypsin-pronase digest of control calf thymus histones and the mixture chromatographed on AA-15, both compounds were resolved from the other peptide (or amino acid) peaks. HPL was eluted in the same fractions as NNPP, HPL and NNPP exhibited identical RF values on silica gel TLC with acidic, alkaline and neutral solvents. CEL was not identified as a product of the reaction between BPL and calf thymus histones.