[Isolation of tissue-specific inhibitors of DNA synthesis (chalones) from rat liver].

Two fractions of non-cytotoxic and tissue-specific inhibitors of 3H-thymidine incorporation into DNA of rat liver regenerating after partial hepatectomy in vitro were obtained by gel filtration on a Sephadex-75 column of the ethanol precipitated aqueous extract. One of these fractions (Ve/Vo = = 2.0; Kav = 0.4) was found to be heterogenous and enriched with proteins with a molecular weight of 17 000-30 000 D. It was biologically active at concentrations exceeding 0.25 mg/ml. The biological activity of the other fraction (Ve/Vo = 3.0; Kav = 1) occurred at concentrations under 0.005 mg/ml. The main component of this fraction was discovered to be a protein with a molecular weight of 17 000 D.