Trimetrexate, a lipid-soluble analogue of methotrexate, appears to enter mammalian cells by passive diffusion, thus circumventing the methotrexate transport system which is frequently a subject for alterations leading to methotrexate resistance. Using a single-step selection protocol with trimetrexate, we have isolated 45 clonal variants and found the majority of them to be selectively resistan...

It has been shown that endothelial NO synthase (eNOS) uncoupling occurs in hypertension and atherosclerosis. However, its causal role in vascular pathogenesis has not been characterized previously. Here, we challenged eNOS preuncoupled hyperphenylalaninemia (hph)-1 mice (deficient in eNOS cofactor tetrahydrobiopterin biosynthetic enzyme GTPCHI) with angiotensin II (Ang II; 0.7 mg/kg per day, 14...

Three sulfonamides and four dihydrofolate reductase inhibitors were tested alone and in combination to determine their in vitro effects on two strains of Toxoplasma gondii grown in MRC5 fibroblast tissue culture. Toxoplasma growth was quantitated by an enzyme immunoassay performed directly on the fixed cultures, and linear regression models were used to quantify the relationship between the opt...

During growth on one-carbon (C1) compounds, the aerobic alpha-proteobacterium Methylobacterium extorquens AM1 synthesizes the tetrahydromethanopterin (H4MPT) derivative dephospho-H4MPT as a C1 carrier in addition to tetrahydrofolate. The enzymes involved in dephospho-H4MPT biosynthesis have not been identified in bacteria. In archaea, the final step in the proposed pathway of H4MPT biosynthesis...

* To whom all correspondence should be addressed. Tel: +234 (0) 703 322 4860; E-mail: [email protected] Parasitological resistance to sulfadoxinepyrimethamine is associated with mutations in parasite dihydrofolate reductase conferring resistance to pyrimethamine and dihydrofolate synthase for sulfadoxine resistance respectively. The prolonged half-life of sulfadoxinepyrimethamine may exert und...

We have also examined similar parameters for several other enzymes; the trend suggests that in these cases there is a correlation between apparent association constant and capacity. These enzymes include yeast glutathione reductase, glucose 6-phosphate dehydrogenase, glutamate dehydrogenase, alcohol dehydrogenase and malate dehydrogenase, Neurospora crassa glutamate dehydrogenase, pig heart iso...

Reduced folate derivatives participate in numerous reactions of bacterial intermediary metabolism. Consequently, the well-characterized enzyme implicated in the formation of tetrahydrofolate--dihydrofolate reductase FolA--was considered to be essential for bacterial growth. However, comparative genomics has revealed several bacterial genome sequences that appear to lack the folA gene. Here, we ...

The intracellular synthesis and retention of polygammaglutamyl derivatives of methotrexate, 4-amino-10methylpteroylglutamate (4-NH2-10-CH3-PteGlul), and their interactions with dihydrofolate reductase were evaluated in the Ehrlich ascites tumor cell in vitro by high pressure liquid chromatography. The accumulation of these metabolites was increased over 5-fold by the addition of 5 m~ L-glutamat...

An enzymatic method for the measurement of methotrexate (MTX) in serum is presented in which the inhibition of the enzyme dihydrofolate reductase by MTX is measured. Reduction of the substrate dihydrofolate by the enzyme and cofactor NADPH is lessened in direct proportion to the amount of MTX present. Measurements can be made in the "therapeutic range" of MTX which corresponds to the 10(-7) to ...