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Dihydrofolate reductase from a methotrexate-resistant subline (R6) of L1210 mouse leukemia cells is activated (i.e. has its catalytic activity increased severalfold) by treatment with (a) sulfhydryl-modifying agents (p-chloromercuribenzoate (pCMB) or 5,5'-dithiobis(2-nitrobenzoic acid], (b) salts (KCl or NaCl), or (c) chaotropes (urea or guanidinium(More)
Biotin derivatives of methotrexate and folate (2-(biotinamido)ethyl-1,3'-dithiopropionyldiaminopentyl methotrexate and/or folate), in which carboxyl groups of the functional components are joined by a disulfide-containing spacer, have been synthesized, purified by DEAE-Trisacryl chromatography, and characterized by high pressure liquid chromatography and(More)
Sephacryl beads containing an immobilized aminopropylcobalamin-transcobalamin-II complex serve as foci for the adherence of L1210 murine leukemia cells. Bead-cell interaction does not occur when (A) nonderivatized beads are used; (B) transcobalamin-II is omitted or presaturated with cyanocobalamin in the preparation of the bead complex; (C) intrinsic factor(More)
Folate is transported into L1210 mouse leukemia cells by the same system that mediates the uptake of methotrexate and reduced folate compounds. This conclusion is supported by the following observations: (a) methotrexate competitively inhibits the influx of folate and the Ki is comparable to the Kt for methotrexate influx; (b) the profile for inhibition of(More)
Methotrexate (MTX) alpha-peptides containing representative neutral (alanine), acidic (aspartic acid), and basic (arginine) amino acids were synthesized by a regiospecific route. Purity and authenticity of MTX-Ala, MTX-Asp, and MTX-Arg were established by TLC, HPLC, elemental analysis, and NMR and absorbance spectra. These peptides were hydrolyzed by(More)
L1210 mouse leukemia cells provide a convenient model for examining the mechanisms and components involved in the active transport of various metabolites and drugs. One of these transport systems exhibits a broad specificity for folate compounds, including 4-amino antagonists such as methotrexate. The primary substrate for this system is(More)