Polymerase competitive

Mechanism of Action Penciclovir triphosphate inhibits HSV polymerase competitively with deoxyguanosine triphosphate. Consequently, herpes viral DNA synthesis and, therefore, replication are selectively inhibited. Therapeutic Effect An antiviral compound that has inhibitory activity against herpes simplex virus types 1 (HSV-1)... 

Inhibits HSV-2 polymerase competitively with deoxyguanosine triphosphate, selectively inhibiting herpes viral DNA synthesis and replication... 

Cidofovir is a cytosine nucleotide analog with in vitro activity against CMV, HSV-1, HSV-2, VZV, EBV, HHV-6, HHV-8, adenovirus, poxviruses, polyomaviruses, and human papillomavirus. In contrast to ganciclovir, phosphorylation of cidofovir to the active diphosphate is independent of viral enzymes. After phosphorylation, cidofovir acts both as a potent inhibitor of and as an alternative substrate for viral DNA polymerase, competitively inhibiting DNA synthesis and becoming incorporated into the viral DNA chain. Isolates with resistance to cidofovir have been selected in vitro these isolates tend to be cross-resistant with ganciclovir but retain susceptibility to foscamet. Clinically significant resistance to cidofovir has not been reported to date. 

The plaque assay is desirable because it is very sensitive and only detects infectious viral particles. However, there are viral agents which cannot be supported by cell lines. In these cases other methods must be used. The polymerase chain reaction (PGR), which amplifies DNA or RNA from viral agents, can be used to detect the presence and quantity of viral agents. The amount of RNA or DNA target in the initial sample can be determined by competitive PGR where the quantity of amplified product is compared to a control PGR product where the initial amount of target is known. Quantification is also possible by an end-point dilution method similar to that used to determine a tissue culture infections dose. PGR methods can be very sensitive however. 

They did find that these compounds behaved kinetically as competitive inhibitors of polymerization of the normal substrates e.g., guanosine 5 -diphosphate. These authors suggested that the successful completion of the polynucleotide phosphorylase reaction requires that the nucleotide be capable of assuming the anti conformation. Also, Kapuler and Reich (53) have found that both 8-bromo- and 8-oxoguanosine 5 -triphosphates are very poor substrates in the E. coli RNA polymerase reaction and are competitive inhibitors with respect to guanosine 5 -triphosphate as a substrate. 

Piatak Jr., M et al. (1993). Quantitative competitive polymerase chain reaction for accurate quantitation of HTV DNA and RNA species. Biotechniques 14,70-80. 

Random copolymers were obtained from the mixture of the two CoA esters in the presence of the polymerase, whereas block copolymers were synthesized when the two monomers were reacted sequentially with the enzyme. In the polymerization of racemic hydroxybutyryl CoA, only the (R)-monomer was polymerized. Furthermore, the presence of the (S)-monomer did not reduce the polymerization rate of the (R)-isomer. These data indicate that the (S)-mono-mer does not act as competitive inhibitor for the polymerase. 

Maeda, H., Fujita, N., and Ishihama, A. (2000) Competition among seven Escherichia coli subunits Relative binding affinities to the core RNA polymerase. Nucleic Acids Res. 28, 3497-3503. 

The answer is c. (Katzung, pp 827-828J Famciclovir is active against herpes simplex and varicella zoster viruses. It is activated by a viral kinase to a triphosphate. The triphosphate is a competitive substrate for DNA polymerase The incorporation of the famciclovir triphosphate into viral DNA results in chain termination. 

The Li+-induced inhibition of the production of the HSV virus may be related to its actions upon viral DNA polymerase production and activity. Li+ reduces both the synthesis of DNA polymerase in tissue culture and the activity of DNA polymerase in vitro, each by about 50%. It has been proposed that Li+ reduces the biosynthesis of viral polypeptides and nucleic acids, and hence inhibits viral DNA replication by competition with Mg2+, a cofactor of many enzymes [243]. However, the inhibitory effect of Li+ on HSV replication in tissue culture is not affected by Mg2+ levels. A more likely hypothesis is the alteration of the intracellular K+ levels, possibly modifying levels of the high-energy phosphate compounds by replacement of either Na+ or K+ in Na+/K+-ATPase [244]. In tissue culture, HSV replication has been shown to be affected by the... 

Related to a class of a,y-diketoacids that has previously been shown to bind to NS5B [64], is the mono-ethyl ester of meconic acid 25. This compound was identified as a selective inhibitor of NS5B HCV polymerase (IC50 = 2.3 pM) and is competitive with the diketoacids. SAR studies have demonstrated the requirement for the carboxylic acid. A variety of different permutations of esters, acids, amides, and decarboxylated compounds were prepared without any improvement in binding affinity or in the cell-based replicon assay [65]. The 4,5-dihydroxypyrimidine-6-carboxylic acids, a hybrid of the a,y-diketoacids and meconic acid, envisioned as chelators of the essential Mg2+ ions in the active site of NS5B, are also active in the polymerase assay (26, IC5o = 5.8pM). While alkylation of the phenol of the hybrid is tolerated, methylation of the heterocyclic hydroxyl groups or the carboxylic acid, as well as decarboxylation, leads to... 

Reversible, non-competitive inhibition of polymerase is also afforded by a series of N-benzoyl pyrrolidines. Substitution on the benzoyl moiety with a para-trifluoromethyl group is optimal in this series. Bulky, hydrophobic groups at the 2-position of the pyrrolidine ring increase activity, and the 5-position tolerates a wide range of substituents, indicative of a solvent exposed portion of the inhibitor. Compound (+)-38, containing a 2-thienyl moiety at the 5-position, has an IC50 of 190 nM in the enzyme assay while its enantiomer is almost 100-fold less active [83]. 

Sestini, R., Orlando, C., Zentilin, L., Gelmini, S., Pinzani, P. et al.. Measuring c-erb B-2 oncogene amplification in fresh and paraffin-embedded tumors by competitive polymerase chain reaction. Clin. Chem. (Winston-Salem, N.C.) 40, 630-636 (1994). 

Two aldehydic nucleotide derivatives have found use as affinity labels. The magnesium salt of (64), formed by oxidation of ATP with periodate, is a competitive inhibitor of pyruvate carboxylase with respect to [Mg. ATP2-],100 and (65), obtained from the / -anomer of 5-formyluridine-5 -triphosphate on treatment with alkali, is a non-competitive and reversible inhibitor of DNA-dependent RNA polymerase from E. coli.101 In each case, addition of borohydride gives stoicheiometric covalent linkage of the nucleotide to the enzyme, with irreversible inactivation. It is thought that condensation with lysine occurs to give a Schiff s base intermediate, which undergoes subsequent reduction. 

Price T, Aitken J, Simpson ER. 1992. Relative expression of aromatase cytochrome P450 in human fetal tissues as determined by competitive polymerase chain reaction amplification. J Clin Endocrinol Metab 74 879-883. 

Nucleic Acid Quantitation Using the Competitive Polymerase Chain Reaction... 

Nucleic acid quantitation using the competitive polymerase chain reaction... 

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