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.