Transport of a nonphosphorylated nucleoside, 5'-deoxyadenosine, by murine leukemia L1210 cells

The mode of transport of a nonphosphorylated adenosine analog, 5'-deoxyadenosine, was studied in murine leukemia L1210 cells. This compound is not subject to the action of intracellular nucleoside-trapping kinases, and its transport can be examined without regard for effects of experimental conditions on kinase activity. Accumulation of 5'-deoxyadenosine was rapid, and nonconcentrative, with equilibrium attained within 12 s at 37 degrees. Kinetic studies were carried out at 20 degrees. We found both a nonmediated (diffusion) and a mediated transport process. The latter had an apparent Km fo 115 micrometer, Vmax = 105 pmol/10(6) cells/min. Uptake of 5'-deoxyadenosine was inhibited by several heterologous nucleosides including adenosine, 2'-deoxyadenosine, thymine riboside, and inosine. Like 2'-deoxyadenosine, 5'-deoxyadenosine was more lipid-soluble than adenosine (from octanol/water partition studies). Compared with 5'-deoxyadenosine, adenosine had a much lower apparent Km (5 micrometer) and a higher Q10 over the 27-37 degrees range (3.0 versus 1.3). Data obtained with adenosine might, however, reflect properties of intracellular adenosine kinase interacting with a transport process.