SUMMARY Inhibition by Methotrexate of dihydrofolate reductase and of the incorporation of deoxynucleosides into DNA has been examined in three mouse ascites cell leukemias which had differ ences in uptake and sensitivity. Dihydrofolate reductase ac tivity in all cell lines was completely inhibited in less than five minutes after the optimal therapeutic dose of Methotrexate. The rate of recovery...

A human T-lymphoblast cell line, CCRF-CEM/R1, resistant to methotrexate by virtue of increased dihydrofolate reductase activity, was grown in stepwise increasing concentrations of methotrexate. This additional selection pressure resulted in a cell line, CCRF-CEM/R2, resistant to methotrexate by virtue of both an elevation of dihydrofolate reductase activity and a marked decrease in methotrexate...

R-Plasmids from a number of trimethoprim-resistant Escherichia coli and Citrobacter sp. were studied after transfer to E. coli K12 hosts. Each was found to specify a dihydrofolate reductase which was resistant to trimethoprim and Methotrexate, and which could be completely separated from the host chromosomal enzyme by gel filtration. Two distinct types of R-plasmid dihydrofolate reductases were...

The kinetics of refolding of Escherichia coli dihydrofolate reductase (EC 1.5.1.3) have been examined upon dilution of unfolded enzyme in 4.5 M urea to 1.29 M urea in 0.02 M phosphate buffer (pH 7.2) at 10 degrees C. Changes in the intrinsic protein fluorescence on refolding are characterized by four phases. Based on changes in the amplitudes of these phases, as a consequence of quenching of th...

DHFR: dihydrofolate reductase MTHFR: methylenetetrahydrofolate reductase INTRODUCTION Psoriasis is a chronic disease that causes erythematous patches with silver plaques and scales, often drastically affecting the quality of life of those afflicted by this disease. Psoriasis is a hyperproliferative disease, which is thought to be the result of a dysregulated immune system, specifically overacti...

Methotrexate (MTX)-resistant mutants of the parasitic protozoan Leishmania have been used as models for the mechanism and genetic basis of drug resistance in trypanosomatids and other cells. Three resistance mechanisms to MTX, a dihydrofolate reductase inhibitor, have been described in Leishmania: decreased uptake and accumulation of MTX via the folate/MTX transporter, amplification and overexp...

Recently, it has been demonstrated that nitrogen mustard-induced N-alkylpurines are excised rapidly from actively transcribing genes, while they persist longer in noncoding regions and in the genome overall. It was suggested that transcriptional activity is implicated as a regulatory element in the efficient removal of lesions. By treating cells or not with the transcription inhibitor alpha-ama...

Adapting metabolic enzymes of microorganisms to low temperature environments may require a difficult compromise between velocity and affinity. We have investigated catalytic efficiency in a key metabolic enzyme (dihydrofolate reductase) of Moritella profunda sp. nov., a strictly psychrophilic bacterium with a maximal growth rate at 2 degrees C or less. The enzyme is monomeric (Mr=18,291), 55% i...