Dihydrofolate reductase DHFR

Overproduction of the chromosomal genes for the dihydrofolate reductase (DHFR) and the dihydroptero-ate synthase (DHPS) leads to a decreased susceptibility to trimethoprim and sulfamethoxazol, respectively. This is thought to be the effect of titrating out the antibiotics. However, clinically significant resistance is always associated with amino acid changes within the target enzymes leading to a decreased affinity of the antibiotics. 

The plasmid vector pTEV-DHFR was used in this study. Internal ribosome entry sequence originated from tobacco etch virus (TEV) was locatai at upstream of dihydrofolate reductase (DHFR) gene. 

Fig. 3. Autoradiograph of SDS-PAGE of in vitro translated dihydrofolate reductase (DHFR) in the wheat germ cell-free protein synthesis systems with (n) 4 pi of ribosome fiaction, (III) 4 pi of 0 -40 % ammonium sulfate fraction, or (IV) 4 pi of 40 - 60% ammonium sulfate fraction, respectively. Lane I is control dihydrofolate reductase produced in the normal wheat germ cell-free protein synthesis system.

Chromosomal mutations in E. coli result in overproduction of dihydrofolate reductase (DHFR). Higher concentrations of trimethoprim, which may not be therapeutically achievable, are therefore required to inhibit nucleotide metabolism. Other mutations lower the affinity of DHFR for trimethoprim. These two mechanisms of resistance may coexist in a single strain, effectively increasing the level of resistance to the antibiotic. 

Folic acid antagonist inhibits dihydrofolate reductase (DHFR) blocks reduction of folate to tetrahydrofolate inhibits de novo purine synthesis results in arrest of DNA, RNA, and protein synthesis... 

We have already used the interactions of methotrexate with dihydrofolate reductase (DHFR) several times within this text to illustrate some key aspects of enzyme inhibition. The reader will recall that methotrexate binds to both the free enzyme and the enzyme-NADPH binary complex but displays much greater affinity for the latter species. The time dependence of methotrexate binding to bacterial DHFR was studied by Williams et al. (1979) under conditions of saturating [NADPH], In the presence of varying concentrations of methotrexate, the progress curves for DHFR activity became progressively more nonlinear (Figure 6.14). The value of kobs from... 

Among these drugs, the dihydrofolate reductase (DHFR) inhibitors are used clinically with a certain amount of success. They belong to two major classes the classical antifolates which feature a polar amino-acid side chain terminus and those containing nonpolar side chains, called lipophilic or nonclassical anti-folates. 

In the context of preparing potential inhibitors of dihydrofolate reductase (DHFR), the group of Organ has developed a rapid microwave-assisted method for the preparation of biguanide libraries (Scheme 6.174) [330]. Initial optimization work was centered around the acid-catalyzed addition of amines to dicyandiamide. It was discovered that 150 °C was the optimum temperature for reaction rate and product recovery, as heating beyond this point led to decomposition. While the use of hydrochloric acid as catalyst led to varying yields of product, evaluation of trimethylsilyl chloride in acetonitrile as solvent led to improved results. As compared to the protic... 

The above model was used to study the binding of methotrexate, and analogues of it, to wild-type and mutant forms of human dihydrofolate reductase (DHFR).29 This turned out to be a particularly difficult test because of the three ionized groups of methotrexate. The overall electrostatic interactions of this inhibitor amount to around -500 kcal/mol and MD trajectories of length more than a ns were required in order to get average... 

Dihydrochalcones, 24 240—241 Dihydrofloriffone, 24 570 Dihydrofolate reductase (DHFR) inhibitors, 26 495-496... 

Dihydrofolate reductases (DHFR), 48, 54, 56 Dimethyl chalcogenides, 131-133 Dimethylselenide, 131-133 Dimethyltellurides, 131-133 Diorgano diselenides, 113 Diorgano ditellurides, 113 Diorganochalcogen(IV) dihalides crystallographic structure, 80f redox reactions, 90 Diorganoselenides... 

SV40 Promoter This is the promoter for expression of the DHFR gene. DHFR The enzyme dihydrofolate reductase (DHFR) is required for nucleotide (thymine) synthesis and cell growth and serves as a selection marker in mammalian cells. 

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