Search

N3-Methyl derivative of 3'-azido-3'-deoxythymidine 5'-triphosphate (Me-AZTTP) showed a potent inhibitory effect on HIV-1 reverse transcriptase using MS2 phage RNA as the template. The inhibition mechanism of MeAZTTP was noncompetitive with respect to any of the template MS2 RNA, dATP and dCTP. On the other hand, MeAZTTP showed a mixed-type inhibition with respect to dGTP and dTTP. These results indicate that MeAZTTP competes not only with dTTP but also with dGTP.

(E)-5-(2-bromovinyl)-2'-deoxyuridine 5'-triphosphate (BVdUTP), known as a specific inhibitor of herpes simplex virus (type 1)-DNA polymerase, was found to be a potent inhibitor of the activity of terminal deoxynucleotidyltransferase (TdT) from calf thymus. BVdUTP was not an efficient substrate of TdT, but it inhibited the incorporation of normal deoxynucleotide substrates in competitive fashion at the nucleotide binding site of TdT molecule. The Ki value for BVdUTP (5 microM) was much less than the Km value for dGTP (83 microM), indicating stronger affinity of the inhibitor to TdT than that of the substrate. These results indicate the usefulness of BVdUTP as a potent inhibitor of TdT for elucidation of the reaction mechanism of this enzyme.

A trypanocidal drug suramin [hexasodium sym-bis(m-amino-benzoyl-m-amino-p-methylbenzoyl-1-naphthylamino-4, 6, 8-trisulfonate)carbamide] was found to be a potent inhibitor of the activities of DNA primase and polymerase alpha from human KB cells. The mechanism of the inhibition by suramin was, however, quite different by these two polymerases. In the case of DNA primase, suramin inhibited competitively the incorporation of a nucleotide substrate, GTP, on the template polydeoxycytidylate, while the polymerase alpha was inhibited competitively by the drug with respect to the template primer (activated DNA). The observed inhibitory effect of suramin on nucleic acid synthesis seems to explain yet unknown mechanism of trypanocidal action of the drug.

The two components of Camellia sinensis (green tea) (i.e., (-)-epigallocatechin gallate and (-)-epicatechin gallate were found to differentially inhibit the activities of reverse transcriptase and cellular DNA and RNA polymerases. The strongest inhibition by these compounds was observed with reverse transcriptase. DNA polymerases alpha and beta were also strongly inhibited. The mode of the inhibition of reverse transcriptase and other DNA polymerases was competitive with respect to the template.primer, whereas the mode the inhibition of RNA polymerase was competitive with respect to the nucleotide substrate.

Ammonium 21-tungsto-9-antimoniate (HPA23), an inorganic condensed ion, was shown to be a potent inhibitor for DNA polymerase alpha but not for beta. It inhibited the activity of mammalian DNA polymerase alpha in noncompetitive fashion with respect to either of deoxynucleotide substrate and template X primer, indicating the presence of a specific binding site for HPA23 on DNA polymerase alpha molecule. The Ki of the alpha polymerase for HPA23 was 24 nM. A possible interaction of HPA23 with DNA polymerase alpha is discussed.

Evans Blue, an anionic dye which has been found to inhibit the replication of human immunodeficiency virus, proved also inhibitory to the DNA polymerases alpha and beta. The mode of inhibition was competitive with respect to the template X primer, and noncompetitive with respect to the deoxynucleoside triphosphate substrates. The inhibitory effect of Evans Blue on DNA polymerases is discussed in relation to that of suramin.

The mechanism of inhibition by aphidicolin of the activity of purified DNA polymerase alpha was studied. In the presence of aphidicolin and activated DNA, DNA polymerase alpha from mouse myeloma did not show Michaelis kinetics with respect to changes in nucleotide substrate concentration (i.e., dGTP & dTTP). A plot of the reaction velocity versus dGTP or dTTP concentration was hyperbolic with an intermediary plateau. The double reciprocal plot was concave downwards, and the Hill plot gave Hill coefficients of less than 1.0 over most of the curve. These results indicate that aphidicolin acts as an allosteric inhibitor for DNA polymerase alpha and that DNA polymerase alpha functions as a multisite enzyme that exhibits negative cooperativity among at least 3 binding sites of the nucleotide substrates (dGTP & dTTP).