Nucleotidase activity in regenerating liver and in clonal strains of hepatoma and pituitary cells in culture.

A nucleotidase of the combined 3'- and 5'-type (nucleotide phosphohydrolase, E.C.3.1.3.31) was present in the cytosol of regenerating rat liver cells, and of rat hepatoma and pituitary cells in culture. The enzyme activity per milligram of cell protein was very similar in regenerating liver and in three of the different cell types. The hepatoma cell strain which showed the slowest growth rate had a three-fold higher basal enzyme activity. After the first days of regenerative growth in rat liver and during early plateau phase of cell growth, there was a 50-120% increase in specific enzyme activity. In the hepatoma cells, the enzyme activities were also compared to the cellular content and synthesis of RNA and DNA. The increase in enzyme activity occurred concomitantly with a reduced incorporation of 3H-thymidine into DNA. The possible physiological role of this nucleotidase in nucleic acid and nucleotide metabolism is discussed.