Nature of rat liver cell sap factors inhibiting the DNA synthesis in tumour cells

Abstract

1. 1. In the previous paper, we reported that the adult rat liver cell extract (sap) inhibits the incorporation of [ 14C]thymidine into DNA of ascites hepatoma cells in culture 3 and that there are at least two inhibitor components in the adult rat liver cell sap, one of which is arginase 6. 2. 2. Arginase is not present in the new-born rat liver, while the thermolabile inhibitor component is present in both the adult and the new-born rat liver. Experimental evidence presented in this paper suggests that the thermolabile inhibitor present in the rat liver cell extracts is thymidine hydrolase and/or phosphorylase. Malignant hepatomas lack both arginase and thymidine-decomposing enzymes. 3. 3. New-born rat liver contains a factor stimulating [ 14C]orotate incorporation into RNA and DNA of the ascites hepatoma cells in culture.