Pyrimidine nucleoside, pseudouridine, and modified nucleoside excretion by growing and resting fibroblasts

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Abstract
We are examining the relationship of RNA metabolism and de novo pyrimidine synthesis as parameters of malignant transformation. These initial experiments on normal hamster embryo fibroblasts have shown that excreted nucleosides are markers for intracellular RNA metabolism. We employed affinity chromatography to concentrate the nucleosides in the medium and sensitive column chromatographic procedures to quantitatively measure them. The excretion of pyrimidine nucleoside from hamster embryo fibroblasts in culture was found to be dependent on the growth stage of the cells, with the greatest accumulation occurring during cell quiescence. The major nucleoside excretion products, uridine and cytidine, were both normal end products of RNA metabolism and the major nucleoside excretion products from cultured cells. The modified nucleosides N‐1‐methylguanosine, N‐2‐methylguanosine, N‐2‐dimethylguanosine, N‐4‐acetylcytidine, N‐1‐methylinosine, pseudouridine, N‐1‐methyladenosine, N‐3‐methylcytidine, and 5‐methylcytidine were found, as were several unidentified nucleosides.