With the current national commitment to cancer research, new and challenging areas of investigation are being planned. Hopefully, this inevitably expanding search into the nature and treatment of malignant tumors will include a continued examination of current chemotherapeutic agents. These standard tumoricidal drugs have proved to be effective in the therapy of numerous cancers despite an inco...

We have compared the relative susceptibility of resting (GO) versus exponentially growing mouse fibroblasts (line 3T6) to methotrexate (MTX) cytotoxicity. Cultures of cells were exposed to different levels of MTX for various intervals. Cloning efficiencies of the cells were then determined in medium containing hypoxanthine and thymidine. We found that growing 3T6 cells exhibit time- as well as ...

Dihydrofolate reductase (DHFR) catalyzes the reduction of dihydrofolate to tetrahydrofolate. The catalytic rate in this system has been found to be significantly affected by mutations far from the site of chemical activity in the enzyme [Rajagopalan, P. T. R, Lutz, S., and Benkovic, S. J. (2002) Biochemistry 41, 12618-12628]. On the basis of extensive computer simulations for wild-type DHFR fro...

A novel trimethoprim resistance gene, designated dfrK, was detected in close proximity to the tetracycline resistance gene tet(L) on the ca. 40-kb plasmid pKKS2187 in a porcine methicillin (meticillin)-resistant Staphylococcus aureus isolate of sequence type 398. The dfrK gene encodes a 163-amino-acid dihydrofolate reductase that differs from all so-far-known dihydrofolate reductases.

A conserved residue at the dihydrofolate binding site of dihydrofolate reductase (EC 1.5.1.3), leucine-54, was replaced with glycine to ascertain the role of this hydrophobic amino acid. The effect of the mutation is both to increase the dissociation rate of dihydrofolate and decrease the rate of hydride transfer thus changing the rate-limiting step in catalysis from product loss (leucine-54) t...

Methotrexate has been in use as an anti-cancer agent for over 60 years. Though inhibition of dihydrofolate reductase is its best known mechanisms of action, its non-dihydrofolate reductase dependent mechanisms disrupt metabolic pathways resulting in a depletion of NAD(P)H and increasing oxidative stress. These mechanisms highlight a novel dependence of cancer cells on their metabolic abnormalit...

The dihydrofolate reductase from Mycobacterium phlei was purified and characterized; it has an Mr of 15 000 and a pI of 4.8. It is competitively inhibited by both methotrexate and trimethoprim, although the affinity is less than for other bacterial dihydrofolate reductases.

A gene encoding a bifunctional homodimeric dihydrofolate reductase-thymidylate synthase (DHFR-TS) was constructed by destroying the stop codon of Escherichia coli dihydrofolate reductase (DHFR) and joining the coding sequences of the monofunctional enzymes by a five amino acid linker. The protein was designed to mimic features of active site proximity and electrostatics in the protozoan DHFR-TS...

The objective of this study was to investigate whether polymorphisms of genes that are involved in one-carbon metabolism (dihydrofolate reductase, methionine synthase reductase, methylenetetrahydrofolate reductase, reduced folate carrier 1 and transcobalamin II) influence DNA methylation in 106 patients with alcoholism. In the multivariate model no genotype showed significant effects on DNA met...