Pyrimidine Biosynthesis in Normal and Transformed Cells

摘要

The authors have developed procedures for sensitive measurement of specific raioactivities of pyrimidine nucleosides excreted from cells in culture. The changes in the observed values reflect dilution of the added isotope through de novo biosynthesis of nonradioactive pyrimidine nucleosides or by shifting and equilibration of other nucleotide pools into the free uridine pool. It is thus possible to monitor uridine biosynthesis occurring in intact cells without destroying or disrupting the cell population. On comparing a series of normal and transformed lines, we have observed several growth dependent patterns of change in specific activity and levels of uridine excretion and the temporal appearance of these changes. Hamster embryo fibroblasts cease pyrimidine biosynthesis at mid-growth while hamster cell line V79 continues to dilute the pyrimidine pool at about 7% of the rate observed during exponential growth at confluence. Both cells exhibit Urd excretion beginning at one-half maximal growth. Passageable normal rat liver cells (IARC-20) also show a cessation of pyrimidine biosynthesis with a prior increase in uridine excretion. (ERA citation 04:045411)