No abstract

The substrate specificity of procaryotic and eucaryotic AppppA-degrading enzymes was investigated with phosphonate analogues of diadenosine 5',5'''-P1,P4-tetraphosphate (AppppA). App(CH2)ppA (I), App(CHBr)ppA (II), and Appp(CH2)pA (III), but not Ap(CH2)pp(CH2)pA (IV), are substrates for lupin AppppA hydrolase (EC 3.6.1.17) and phosphodiesterase I (EC 3.1.4.1). None of the four analogues is hydrolyzed by bacterial AppppA hydrolase (EC 3.6.1.41), and only analogue III is degraded by yeast AppppA phosphorylase (EC 2.7.7.53). The analogues are competitive inhibitors of all four enzymes. The affinity of analogue IV is 3-40-fold lower than that of analogues I-III for all four enzymes. Introduction of one methylene (as in I and III) [or bromomethylene (as in II)] group into AppppA results in a 3-15-fold increase of its affinity for lupin and Escherichia coli AppppA hydrolases. The same modifications only negligibly (10-30%) affect its affinity for yeast AppppA phosphorylase and decrease its affinity for lupin phosphodiesterase I about 2.5-fold. The data provide further evidence for the heterogeneity among catalytic sites of all four AppppA-degrading enzymes.

It is demonstrated here that rat liver DNA polymerase /I catalyzes the pyrophosphorolysis reaction with pyrophosphate (PP<) and its analogues. The substrate specificity of the PPi-binding site of several DNA polymerases was investigated. It was discovered that the ability of DNA polymerases to utilize PPi analogues instead of PPi in the pyrophosphorolysis reaction was markedly restricted. Only imidodiphosphate and methylenediphosphonate were demonstrated as participating in this process. Oxodiphosphonate and phosphonoformate inhibited DNA synthesis, but probably not via the interaction with the PPi-binding site of DNA polymerases.

A series of pyrophosphoryl (Z)-(phosphonomethoxy)but-2-enyl derivatives of pyrimidines and purines 9a-d and the corresponding phosphonates 10a-d were synthesized. The prepared compounds contain the phosphonate group as an alpha-phosphate mimic as well as an acyclic residue emulating the sugar moiety in 2',3'-dideoxy-2',3'-didehydronucleoside 5'-triphosphates known as highly potent chain terminators of DNA polymerases. Phosphonates 10a-d were obtained by alternative alkylations of the nucleic bases followed by condensation with ethyl [[(p-tolylsulfonyl)oxy]methyl]phosphonate. Pyrophosphorylation of 10a-d afforded phosphonate diphosphates 9a-d. Their substrate properties were evaluated in cell-free systems containing various DNA polymerases including viral reverse transcriptases. Compounds 9a-d manifested good terminating substrate properties toward HIV-1 and AMV reverse transcriptases. They exhibited high selectivity and were not recognized by human DNA polymerases alpha and epsilon, DNA polymerase beta from rat liver, Escherichia coli DNA polymerase I, and HSV-1 and CMV DNA polymerases. Phosphonates 10b-d displayed no activity in HIV-1-infected MT-4 cells cultures; 10a was moderately effective (ED50 = 9 microM).

The acylamino acid esters of nucleoside 5'-phosphates are synthesized via condensation of N-(N'-acylaminoacyl) imidazoles with nucleoside 5'-phosphates. The PMR and CD spectra of the esters obtained are studied. The 3'-isomers of the substances under study are observed to have a shift in the conformational N in equilibrium S equilibrium of the carbohydrate moiety in favour of the S-form as compared to the initial nucleosides and their 2'-acyl esters.