title: Photoinactivation of the methotrexate transport system of L1210 cells by 8-azidoadenosin 5'-monophosphate.
abstract: Methotrexate transport in L1210 cells is mediated by a carrier protein that can bind organic and inorganic phosphate compounds in addition to the various folate substrates. The photoaffinity labeling agent, 8-azidoadenosine 5'-monophosphate (8-azido-AMP), also interactis (Ki = 140 microM) with the receptor site for this transport system, and upon irradiation with ultraviolet light, irreversibly inhibits methotrexate uptake. Protection against this inactivation is afforded by either a substrate (methotrexate) or a competitive inhibitor (inorganic phosphate). The light-induced reaction proceeds rapidly (t1/2 = 2 min at 23 degrees C under the conditions described) and produces half-maximal reduction in the transport rate when the 8-azido-AMP concentration is 65 microM. complete photoinactivation of methotrexate transport could not be obtained from a single exposure to 8-azido-AMP (up to 1.0 mM), but it could be achieved by the repetitive illumination of cells in a fresh medium. The phosphate and folate/adenine transport systems of L1210 cells are not affected by irradiation in the presence of 8-azido-AMP.
mesh_terms: D000227:Adenine Nucleotides / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001386:Azides; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D007700:Kinetics; D007939:Leukemia L1210 / Q000378:metabolism*; D008727:Methotrexate / Q000378:metabolism*; D051379:Mice; D010710:Phosphates / Q000494:pharmacology; D010777:Photochemistry; D013835:Thiamine Pyrophosphate / Q000494:pharmacology
chemical_list: D000227:Adenine Nucleotides; D001386:Azides; D002352:Carrier Proteins; D010710:Phosphates; D000249:Adenosine Monophosphate; C021291:8-azidoadenosine 5'-monophosphate; D013835:Thiamine Pyrophosphate; D008727:Methotrexate