P C Elwood

TL;DR: The hypothesis that the membrane-associated folate-binding protein of human cells participates in the transport of folates under physiologic conditions is supported.

TL;DR: The studies indicate that the folate transport system is probably regulated by the extracellular folate concentration through changes in intracellular metabolite levels.

TL;DR: The purified membrane-associated and soluble folate-binding proteins give single bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with apparent values of 50,000 and 40,000, respectively and exceed the reported increase in affinity of methotrexate polyglutamates for dihydrofolate reductase.

TL;DR: Characterization of this membrane-associated protein indicated that it was soluble in solutions containing Triton X-100, was capable of binding folic acid as well as methotrexate, had an apparent Mr of 160,000 by gel filtration in the presence of Trit on X- 100, and was precipitated by antiserum to human placental folate receptor.

TL;DR: Differences in the levels and specific activities of the two folate-binding proteins of cells exposed to cycloheximide compared with simultaneous controls after pulsing with [35S]methionine suggest that, whereas the cell-associated folATE-binding protein is probably produced by de novo protein synthesis, the soluble folates seems to be produced from a cellular pool of an already synthesized protein.