[Demonstration of pyrimidine nucleoside phosphorylases in breast cancer]

Two pyrimidine phosphorylase activities have been isolated from the cytosol of cultivated MCF-7 cells of a human breast cancer, by ion exchange chromatography. Both enzymes are responsible for the cleavage of thymidine into thymine and deoxyribose-1-phosphate, for the synthesis of thymidine and for the transfer of deoxyribose from d-uridine to thymine. These activities are likely to participate in the regulation of the pool of pyrimidine nucleosides required for DNA synthesis.