METABOLISM OF HISTONES IN MALIGNANT TISSUES AND LIVER OF THE RAT AND MOUSE

Abstract

The relative amounts of incroporation in-vivo of L-lysine, and in 1 experiment L-arginine, into different histone fractions from Krebs ascites and a lymphoma ascites cells of mice and a "solid" tumor and liver of rats have been determined. No marked differences in the incorporations of the amino acids into the fractions F1, F2a, F2b and F3 from the tumors were generally observed, although in some experiments there was a greater incorporation into fraction F2b, which could be decreased by further purification. In the tumors, the incorporations into all cell protein fractions obtained were approximately the same, indicating that the amount of incorporation was that required for the increase of cell mass. In rat liver, the incorporations into fractions F1, F2a and F3 were not greatly different. That into fraction F2b was variable. The incorporation into the histone fractions was much less than that into the acid-insoluble nuclear residue, indicating that considerable turnover of amino acids in the latter occurs. The decrease in radioactivity of labelled histone and acid-insoluble nuclear protein in-vivo during several days confirmed the relatively small turnover of the histone fraction. The time taken for liver whole histone to lose half its radioactivity was about 1 week. A histone fraction of slower metabolism was also detected. It is concluded that no appreciable turnover of protein occurs in any one histone fraction, the somewhat higher values obtained in certain cases being associated with acidic impurities. The apparently high rate of incorporation into histone of resting liver is discussed in relation to recent evidence on DNA metabolism of resting liver.