Transport and countertransport of thymidine in ATP depleted and thymidine kinase-deficient novikoff rat hepatoma and mouse L cells: Evidence for a high Km facilitated diffusion system with wide nucleoside specificity

摘要: Incubation of cultured Novikoff rat hepatoma and mouse L cells in a glucose-free basal medium containing 5 mM KCN iodoacetate for about 10 minutes resulted complete depletion the ATP. ATP-depleted wild type or thymidine kinase-deficient sublines took up rapidly from without concentrating it intracellularly, exhibited countertransport thymidine. Thus uptake was by facilitated diffusion. This transport system differs substrate-specific, low-Km (0.5 muM] previously described various types that exhibits an at least 100-fold higher Km transports equally well ribo- deoxyribonucleosides. The results suggest rate-limiting step incorporation into nucleotide pool is phosphorylation rather than transport, possess two systems, diffusion with low substrate specificity second which involves kinase.