Formation of cyclopyrimidines via the direct effects of gamma radiation of pyrimidine nucleosides

Continuing our study of the direct effects of gamma radiation on DNA and its model compounds, we have isolated and characterized quantitatively an important lesion formed by irradiating pyrimidine 2'-deoxyribonucleosides in frozen aqueous solution. We report here the formation of 5',6-cyclo-5,6-dihydropyrimidine nucleosides via hydrogen abstraction at C5' of the osidic moiety with subsequent intramolecular attack at C6 of the base. We have so far managed to isolate six of the possible eight diastereomers of 5',6-cyclo-5,6-dihydrothymidine, and all four possible 5',6-cyclo-5,6-dihydro-2'-deoxyuridines formed by irradiation of 2'-deoxycytidine. Also presented is a detailed discussion of the configurational analysis of each isomer based on 1H NMR data.

Free radical generation by ultrasound in aqueous solutions of nucleic acid bases and nucleosides: an ESR and spin-trapping study

Direct evidence for the detection of intermediate radicals of nucleic acid constituents induced by ultrasound in argon-saturated aqueous solution is presented. The method of spin trapping with 3,5-dibromo-4-nitrosobenzene sulphonate, which is a water-soluble, non-volatile, aromatic nitroso spin trap, combined with ESR, was used for the detection of sonochemically induced radicals. Spin adducts were also generated by OH radicals produced by UV photolysis of aqueous solution containing H2O2. ESR spectra observed from these photolysis experiments were identical to those after sonolysis. The ESR spectra of the spin adducts suggest that the major spin-trapped radical of thymine and thymidine was the 5-yl radical, and that of cytosine, cytidine, uracil, and uridine was the 6-yl radical. To compare the radicals induced by sonolysis and photolysis, the decay of the ESR spectra of the thymine and thymidine spin adducts was investigated. The decay curves of thymine and thymidine after sonolysis indicated biphasic decay. However, after photolysis the spin adducts from both compounds showed very little decay. These results suggest that the observed spin adducts in the sonolysis of pyrimidine bases and nucleosides were formed by OH radical and H atom addition to the 5,6 double-bond.

Rate of incorporation of radiolabelled nucleosides does not necessarily reflect the metabolic state of cells in culture: effects of latent mycoplasma contamination

In response to cell-free conditioned medium derived from the human bladder carcinoma line T24 (T24 SN), we found greatly reduced incorporation of tritiated thymidine and uridine ([3H]TdR, [3H]UR) by the human carcinoma lines UCHNCu (small-cell lung carcinoma) and LS174T (colon carcinoma). The effect was not due to an excess of nucleosides or cytokines known to be present in T24 SN. Cell-cycle distribution, increase in cell numbers, and de novo nucleoside synthesis in the indicator cells were only slightly altered. This was in contrast to the gross reduction in [3H]TdR/[3H]UR incorporation and seemed to indicate selective downregulation of pyrimidine-salvage pathways, despite ongoing polynucleotide synthesis. Spontaneous [3H]TdR uptake remained low for several passages in vitro but was readily restored by pharmacological inhibition of de novo pathways with 5-fluoro-deoxy-uridine (5-FUdR). This suggested a stable but reversible regulatory effect of T24 SN on the pyrimidine metabolism of the indicator cells. Further investigation showed degradation of [3H]TdR by a particle-bound activity in T24 SN. Mycoplasma contamination of T24 had not been detectable using standard cultural and staining methods, but became apparent when T24-cell lysates were hybridized with a recently described DNA probe (Goebel & Stanbridge, 1984). We conclude that latent mycoplasma contamination can stimulate changes in cellular pyrimidine metabolism. Our results provide an example for latent mycoplasma infection mimicking metabolic changes in cultured cells by direct interference of a microbial enzyme with the assay system. We describe a rapid and simple bioassay to detect and distinguish particle-associated and soluble phosphorylase activity by [3H]TdR degradation. It may be a useful screening assay for mycoplasma contamination in tissue culture.

Reactions of 5-bromo substituted pyrimidine nucleosides with aqueous alkalies: kinetics and mechanisms

Kinetics for the parallel and consecutive steps of the reactions of 5-bromocytidine, 5-bromouridine and its 5'-O-methyl and 2',3'-O-isopropylidene derivatives with aqueous alkalies were studied by LC. The mechanisms of the partial reactions involved are discussed.

Bagougeramines A and B, new nucleoside antibiotics produced by a strain of Bacillus circulans. II. Physico-chemical properties and structure determination

Bagougeramines A and B obtained as sulfates were soluble in water and positive to Sakaguchi, chlorine-tolidine and ninhydrin color reactions. Their structures were determined by acid hydrolysis and spectroscopic analysis. Structurally they were closely related to gougerotin and they contained the guanidino-D-alanine instead of the serine residue in gougerotin. Bagougeramine B had the spermidine instead of the 6'-NH2 in structure of bagougeramine A.

New adducts of chloroethylene oxide and chloroacetaldehyde with pyrimidine nucleosides

Pyrimidine nucleosides were treated with chloroethylene oxide (CEO) and 2-chloroacetaldehyde (CAA) in methanol and, following trimethylsilylation, the products were analysed by combined gas chromatography-mass spectrometry (GC-MS). Reaction of CEO with 2'-deoxycytidine gave 3,N4-etheno-2'-deoxycytidine and diadduct isomers in which a 1-hydroxy-2-chloroethyl group was substituted for hydrogen on either deoxyribose hydroxyl group. When the N-3-position of 2'-deoxycytidine was blocked by a methyl group, CEO or CAA added a 2-chlorovinyl group at the exocyclic N4 amino nitrogen, as evidenced by a pair of cis/trans isomers. Reaction of 3-methylcytidine and CEO also gave the cis/trans 2-chlorovinyl base adducts, as well as six isomers with a 1-hydroxy-2-chloroethyl group attached to ribose and nine isomeric diadducts, which are possibly positional and optical isomers. Although CEO and CAA were less reactive towards uracil in 3-methyluridine than to cytosine in 3-methyl(deoxy)-cytidine, both electrophiles were able to alkylate 3-methyluridine on ribose, yielding 1-hydroxy-2-chloroethyl derivatives. These data suggest that CEO and CAA may also yield non-cyclic adducts with cytosine in double-stranded DNA where the N-3 position is of low accessibility. Such adducts are of interest in view of their potential promutagenic properties. The data also imply a new mechanism of reaction of CEO with nucleophiles.

Inhibitors of the biosynthesis and processing of N-linked oligosaccharides

A number of glycoproteins have oligosaccharides linked to protein in a GlcNAc----asparagine bond. These oligosaccharides may be either of the complex, the high-mannose or the hybrid structure. Each type of oligosaccharides is initially biosynthesized via lipid-linked oligosaccharides to form a Glc3Man9GlcNAc2-pyrophosphoryl-dolichol and transfer of this oligosaccharide to protein. The oligosaccharide portion is then processed, first of all by removal of all three glucose residues to give a Man9GlcNAc2-protein. This structure may be the immediate precursor to the high-mannose structure or it may be further processed by the removal of a number of mannose residues. Initially four alpha 1,2-linked mannoses are removed to give a Man5 - GlcNAc2 -protein which is then lengthened by the addition of a GlcNAc residue. This new structure, the GlcNAc- Man5 - GlcNAc2 -protein, is the substrate for mannosidase II which removes the alpha 1,3- and alpha 1,6-linked mannoses . Then the other sugars, GlcNAc, galactose, and sialic acid, are added sequentially to give the complex types of glycoproteins. A number of inhibitors have been identified that interfere with glycoprotein biosynthesis, processing, or transport. Some of these inhibitors have been valuable tools to study the reaction pathways while others have been extremely useful for examining the role of carbohydrate in glycoprotein function. For example, tunicamycin and its analogs prevent protein glycosylation by inhibiting the first step in the lipid-linked pathway, i.e., the formation of Glc NAc-pyrophosphoryl-dolichol. These antibiotics have been widely used in a number of functional studies. Another antibiotic that inhibits the lipid-linked saccharide pathway is amphomycin, which blocks the formation of dolichyl-phosphoryl-mannose. In vitro, this antibiotic gives rise to a Man5GlcNAc2 -pyrophosphoryl-dolichol from GDP-[14C]mannose, indicating that the first five mannose residues come directly from GDP-mannose rather than from dolichyl-phosphoryl-mannose. Other antibodies that have been shown to act at the lipid-level are diumycin , tsushimycin , tridecaptin, and flavomycin. In addition to these types of compounds, a number of sugar analogs such as 2-deoxyglucose, fluoroglucose , glucosamine, etc. have been utilized in some interesting experiments. Several compounds have been shown to inhibit glycoprotein processing. One of these, the alkaloid swainsonine , inhibits mannosidase II that removes alpha-1,3 and alpha-1,6 mannose residues from the GlcNAc- Man5GlcNAc2 -peptide. Thus, in cultured cells or in enveloped viruses, swainsonine causes the formation of a hybrid structure.(ABSTRACT TRUNCATED AT 400 WORDS)

Nucleoside phosphorylase activity of Octopus vulgaris hepatopancreas

From a research on partially purified extracts of Octopus vulgaris hepatopancreas a number of properties of the nucleosidase present in such extracts have been defined, such as enzyme affinity towards different purine and pyrimidine ribo- and deoxyribo-nucleosides. The phosphorolytic mechanism of action of the Octopus enzyme system is similar to the mechanism already known for many nucleosidases from animal tissues. The possibility is envisaged of two different nucleosidases being present, one specific for ribonucleosides, with an acid optimum pH, and the other one for deoxyribonucleosides, with an alkaline pH optimum. Adenosine deaminase also appears to be a component of Octopus hepatopancreas.

Tunicamycins, streptovirudins, and corynetoxins, a special subclass of nucleoside antibiotics

Tunicamycins, streptovirudins, and very recently, corynetoxins have been determined to be structurally related nucleoside antibiotics. Because of their special biological activity as inhibitors of protein glycosylation and their relatively complicated chemical structures, which differ from the common nucleoside antibiotics, they can be grouped together as a special subclass. A general specification system based on structural characteristics is included. The complete separation of the natural complex is still problematical, but seems to be necessary because differences in the biological activities of the individual components were observed.

Effects of streptovirudin on influenza viruses type A and B: inhibition of the lipid-linked oligosaccharide synthesis of fowl plague virus

Antibiotics of the streptovirudin complex (SV) inhibited the growth of influenza A and B viruses such as influenza A/fowl plague virus (FPV), strain Weybridge (Hav1 Neq1), influenza A/England 42/72 (H3N2), influenza A/Port Chalmers 1/73 (H3N2), influenza B/Leningrad 235/74, influenza B/Tokyo 7/66, and influenza B/Jamagata in chick embryo cell (CEC) cultures, in permanent canine kidney cells (MDCK), and in suspended fragments of chick embryo chorioallantoic membranes (CAM). As revealed by spectrophotometric turbidity measurements, SV completely inhibited the FPV-induced cytopathic effect (CPE). A 99.99% reduction of infectious virus yield was obtained in one-step growth cycle experiments and in the plaque reduction test. The haemagglutination inhibition titres of influenza viruses in suspended CAM fragment cultures in the presence of SV drugs were also substantially reduced. The incorporation assays indicated that SV exhibited no effect on virus-induced RNA synthesis, but influenced virus maturation by inhibition of lipid-linked oligosaccharide synthesis. A partial protection from infection was found in influenza virus A/England infected mice.

Correlation between glycosyl torsion angle and sugar ring pucker does not always exist

A survey of the conformational parameters of deoxypyrimidine nucleosides and nucleotides shows that the correlation between glycosyl torsion angle and sugar pucker, which has often been considered to be well-established, does not always exist. This may be of significance when interactions between DNA and other molecules are considered.

[Induction of immune interferon by erythrogenic toxins A and B from Streptococcus pyogenes]

By interaction of streptococcal erythrogenic toxins A and B with chick embryo fibroblasts and human amnion (FL) cells an antiviral interferon-like factor was secreted. It inhibited the replication of vesicular stomatitis, vaccinia and Mengo viruses. The streptococcal toxin type B was 50 times more cytotoxic for both cell cultures in comparison with streptococcal toxin A. The maximum tolerated doses of the two types of streptococcal toxins induced approximately the same antiviral protection effect. The production curve of the antiviral factor showed a maximum at the 12th hour after incubation at 37 degrees C with graduate decrease up to the 24th hour using a 6 hours induction time. The interferons induced by the streptococcal erythrogenic toxins A and B were thermostable at 56 degrees C for 30 min and were partially destroyed at pH 2 as tested against Mengo virus in FL cells. The antiviral effect could be reversed by addition of streptococcal erythrogenic toxin A at the maximum tolerated dose simultaneously with the glycosylating inhibitors streptovirudin and D-glucosamine by 90 and 100 per cent, respectively.

Pyrimidine ribonucleoside phosphorylase activity vs 5- and/or 6-substituted uracil and uridine analogues, including conformational aspects

The pyrimidine ribonucleoside phosphorylase from Salmonella typhimurium phosphorylyses 6-methyluridine, a uridine analogue sterically constrained to the syn conformation about the glycosylic bond, as effectively as uridine itself. In conjunction with the observation that 3-methyluridine is a very poor substrate compared to 5-methyluridine and 5,6-dimethyluridine, it follows that the phosphorolysis reaction involves the initial conversion of uridine, and other 5-substituted uridines (including 5-fluorouridine), to the syn conformation during interaction with the enzyme. Furthermore, and consistent with the foregoing, the enzyme recognizes as substrates, to varying degrees, the N(3)-ribosides of xanthine and uric acid, and will also catalyze the formation of these ribosides from the corresponding purines, which may be considered formally as 5,6-disubstituted uracils. Similar observations are reported for the synthetic 5,6-trimethyleneuridine. The enzyme does not, however, recognize 6-methyluracil and 5,6-tetramethyleneuridine in the reverse, synthetic, reaction. The conformational aspects of these reactions are discussed. Since it was previously shown that 6-methyluridine is an equally effective substrate for the pyrimidine phosphorylase of primary rabbit kidney cells, at least some of these conformational requirements apply to the enzyme from mammalian sources, and are consequently of relevance in the design of chemotherapeutic agents, for which some examples are cited.

E.S.R. of spin-trapped radicals in aqueous solutions of pyrimidine nucleosides and nucleotides. Reactions of the hydroxyl radical

Free radicals produced by the reactions of OH radicals with ribose phosphates, pyrimidine nucleosides and nucleotides in aqueous solutions have been investigated by e.s.r. and spin-trapping techniques. OH radicals were generated by U.V. -photolysis of hydrogen peroxide and short-lived free radicals of the samples were spin-trapped by t-nitrosobutane and identified by e.s.r. spectroscopy. For ribose-5'-phosphate and 2' -deoxyribose-5' -phosphate, e.s.r. spectra observed consisted mainly of singles due to -C(5')H2 radicals which were initiated by H-abstraction from the sugar at the C-4' position and formed by the radical transfer to the C-5' position. It has also been shown that OH radicals abstract a hydrogen atom from the sugar at C-1' and C-5' positions. For cytidine, deoxycytidine, 5'-CMP, 3' -CMP and 5' -dCMP, four radicals have been observed and for uridine, deoxyuridine, 5' -UMP, 3' -UMP and 5' -dUMP, the existence of at least three radical species have been established. In contrast to the case of ribose phosphates, no signals due to -C(5')H2 radicals were detected for pyrimidine nucleosides and nucleotides. The results are discussed in relation to a recent mechanism which described OH-induced strand breaks of DNA.

Biological activities of isolated tunicamycin and streptovirudin fractions

The nucleoside antibiotics tunicamycin and streptovirudin were separated by high-performance liquid chromatography into a series of 256-nm-absorbing peaks. Most of the streptovirudin peaks eluted from a Biosil ODS column earlier than those of tunicamycin, indicating that they were less hydrophobic. With the exception of the first peak, 17 other tunicamycin peaks were potent inhibitors of the formation of dolichylpyrophosphoryl-N-acetylglucosamine with 50% inhibition of the solubilized GlcNAc-1-P transferase requiring about 10 ng of antibiotic per mL. These fractions also inhibited the synthesis of dolichylphosphorylglucose, but in these cases about 500 ng/mL was necessary to achieve 50% inhibition. In MDCK cells in culture, the four major tunicamycin peaks inhibited the incorporation of [2-(3)H]mannose into protein by 50% at about 0.2-0.5 microgram/mL, but [3H]leucine incorporation into protein was unaffected, except at high levels of antibiotic (5-10 microgram/mL). Essentially the same results were observed with the streptovirudin fractions except that they were somewhat less active and some inhibition of protein synthesis was observed with several of these peaks.

Gold complexes of purine and pyrimidine nucleosides

the reactions of chloroauric acid (HAuCl4) with inosine=ino, guanosine=guo, triacetylinosine=trino, triacetylguanosine=trguo, and cytidine=cyd were studied. Complexes of AU(III) and AU(I) with these nucleosides have been isolated from the reactions at different pH values in aqueous and in methanolic solutions. The Au(I) complexes were obtained by reducing Au(III) with 1-ascorbic acid in aqueous solutions. All the isolated complexes were characterized by elemental analyses, conductivity measurements, IR, 1H nmr, and esr spectra. The Au(III) complexes correspond to the general formulae [Au(nucl)2Cl2]Cl, Au(nucl)Cl3, and Au(nucl-H+Cl2, while the Au(I)complexes are of the au(nucl)2Cl type, where nucl represents the above nucleosides. In the complex with the composition (AucydCl2]2 that was isolated from aqueous solutions, the Au atom is believed to be in the (II) oxidation state. Possible structures for all the isolated complexes based on the experimental data are proposed and discussed.

Complex formation between spin-labeled polyuridylic acid and pyrimidine nucleosides

Complex formation between poly (U) and pyrimidine nucleosides, uridine and cytidine, was observed using spin labeling technique. The binding of these nucleosides with poly (U) takes place within a narrow range of their concentration and is characterized by a relatively strong cooperativity. It is shown, that both hydrogen bonding and stacking interaction contribute to the complex stability. Some thermodynamic parameters of the process were obtained from the binding isotherms. At 21 degrees C the equilibrium constants for nucleation were found to be 0.23 M-1 and 0.42 M-1, and those for chain growth 2.63 M-1 and 2.19 M-1 for uridine and cytidine respectively. Complex formation of poly (U) with adenosine was also studied by spin labeling method.