title: Influx of 5'-deoxy-5'-methylthioadenosine into HL-60 human leukemia cells and erythrocytes.
abstract: The influx of 5'-deoxy-5'-methylthioadenosine (MeSAdo) into human HL-60 leukemia cells and erythrocytes was characterized in order to determine whether it is facilitated by the nonspecific nucleoside carrier system or by a separate transporter, as suggested by other reports. Initial velocities were measured at room temperature by means of inhibitor-stop and oil-stop assays. MeSAdo influx was strongly inhibited by Ado, dAdo, and nucleoside transport inhibitors including nitrobenzylthioinosine and dipyridamole. Ade was inhibitory only at concentrations in excess of 1 mM. Loss of nucleoside transport capacity during differentiation of HL-60 cells was accompanied by a corresponding decrease in MeSAdo influx rates. These results indicate that MeSAdo influx was mediated by the nonspecific nucleoside transport system. The kinetic data were consistent with a single saturable carrier and yielded Km values of 74 and 184 microM and Vmax values of 424 and 48 pmols/10(6) cells/min with HL-60 cells and erythrocytes, respectively, after correction for a substantial passive diffusion component, which accounted for over 50% of the influx of 1 mM MeSAdo. The passive diffusion of MeSAdo in the presence of a transport inhibitor was not rate-limiting for the salvage of 50 microM MeSAdo to methionine when HL-60 cells were cultured in methionine-deficient medium. The large contribution of passive diffusion to the influx of MeSAdo is consistent with its unusually high octanol/water partition ratio (5.7-fold greater than that of Ado).
authors.forename: J D
authors.initials: JD
authors.lastname: Stoeckler
authors.forename: S Y
authors.initials: SY
authors.lastname: Li
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D003839:Deoxyadenosines; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D015470:Leukemia, Myeloid, Acute; D013872:Thionucleosides / Q000097:blood / Q000378:metabolism*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D003839:Deoxyadenosines; D013872:Thionucleosides; D014665:Vasodilator Agents; C008500:5'-methylthioadenosine; D000241:Adenosine