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Biomedical subjects

M Leng

Publications and source records attributed to M Leng.

At least 109 records · Page 6Linked to original sources
PubMed1985

Reaction of DNA with a mutagenic 3-N,N-acetoxyacetylamino-4,6-dimethyldipyrido[1,2-a:3',2'- d]imidazole (N-AcO-AGlu-P-3) related to glutamic acid pyrolysates.

3-Amino-4,6-dimethyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-3), an analog amine of the potent genotoxic Glu-P-1 isolated from a glutamic acid pyrolysate, has been chemically synthesized. Glu-P-3 was found much more mutagenic than Glu-P-1 to S. typhimurium TA 98 and TA 100 with S-9 mix. 3-N,N-acetoxyacetylamino-4,6-dimethyldipyrido[1,2-a:3',2'-d] imidazole (N-AcO-AGlu-P-3), a possible metabolite of Glu-P-3, binds covalently to the C-8 position of guanine residues in DNA. The binding induces large conformational changes of the macromolecule.

DNA↗
PubMed1985

Immunological titration of 3-N-acetyl-hydroxyamino-4,6-dimethyldipyrido(1,2-a:3',2'-d) imidazole-rat liver DNA adducts.

Antibodies to N-(guanosin-8-yl)-3-N-acetylamino-4,6-dimethyldipyrido(1,2-a :3',2'-d)imidazole were elicited in rabbits by immunization with a conjugate formed between this compound and bovine serum albumin. The specificity of the antibodies was studied by radioimmunoassay. These antibodies were used to titrate the adducts formed in liver DNA of rats treated with 3-N-acetyl-hydroxyamino-4,6-dimethyldipyrido(1,2-a:3',2'-d)imidazo le,p6 a supposed metabolite of the mutagenic amine 3-amino-4,6-dimethyldipyrido(1,2-a:3',2'-d)imidazole (Glu-P-3). It is found that Glu-P-3 residues are covalently bound to the C8 of guanine in acetylated form (70%) and deacetylated form (30%).

Animals↗
PubMed1984

Thermal stability of the Z-conformation of the tetranucleoside triphosphate (m5dC-dG)2.

The tetranucleoside triphosphate d(m5C-G)2 has been studied in solution by circular dichroism and 31P nuclear magnetic resonance as a function of temperature, in presence of 3 M NaClO4. It is shown that in such high ionic strength d(m5C-G)2 may adopt a Z-like conformation for temperatures lower than 5 degrees C. At these temperatures, another conformation, in slow equilibrium with the Z-like one, is also detected. Increasing the temperature leads to a transition from the Z-like conformation to intermediate forms before melting. It is demonstrated that these intermediates are not the B form.

Circular Dichroism↗
PubMed1984

Electron microscopic measurement of chain flexibility of poly(dG-dC).poly(dG-dC) modified by cis-diamminedichloroplatinum(II).

The antitumor drug cis-diamminedichloroplatinum (II) (cis-Pt) forms bidentate adducts with guanine residues of poly(dG-dC).poly(dG-dC). The secondary structure of the polymer is altered. In this work, high resolution pictures of naked molecules, obtained by dark field electron microscopy reveal DNA chain distortions with radii as small as 30 A. The extent of distortion increases with the drug/nucleotide ratio (rb). These alterations of the secondary structure are responsible for the apparent shortening of the molecules. Measurements of the persistence lengths of the polymer as well as the end-to-end distances of elementary segments of various lengths, are obtained from digitized electron micrographs. The measurements are used to monitor and quantify the observed modifications of polymer structure upon cis-Pt binding at various rb or incubation times. Poly(dG-m5dC).poly(dG-m5dC) in the B and Z forms have different persistence lengths. In the B form, this polymer is more altered by cis-Pt than in the Z one.

Cisplatin↗
PubMed1984

Conformational changes induced in DNA by the in vitro reaction with the mutagenic amine: 3-N,N-acetoxyacetylamino-4,6-dimethyldipyrido (1,2-a: 3', 2'-d) imidazole.

The conformation of synthetic or natural DNAs modified in vitro by covalent binding of N-AcO-A-Glu-P-3 was investigated by fluorescence and circular dichroism. In all cases, substitution occurs mainly on the C8 of guanine residues. In modified poly(dG-dC).poly(dG-dC) or poly(dA-dC).poly(dG-dT) in B conformation, A-Glu-P-3 residues interact strongly with the bases whereas in Z conformation these residues are largely exposed to the solvent and interact weakly with the bases. A-Glu-P-3 and N-acetyl-2-aminofluorene (AAF) residues are equally efficient to induce the B-Z transition of poly(dG-dC).poly(dG-dC) and of poly(dA-dC).poly(dG-dT). Modifications of poly(dG).poly(dC) and calf thymus DNA indicate strong interactions between A-Glu-P-3 and the bases.

Animals↗
PubMed1984

Immunological and spectroscopic studies of poly(dG-dC).poly(dG-dC) modified by cis-diamminedichloroplatinum(II).

The conformational changes induced by the binding of cis-diamminedichloroplatinum(II) to poly(dG-dC).poly(dG-dC) have been studied by reaction with specific antibodies, by circular dichroism and 31P nuclear magnetic resonance. Polyclonal and monoclonal antibodies to Z-DNA bind to platinated poly(dG-dC).poly(dG-dC) at low and high ionic strength. Antibodies elicited in rabbits immunized with the platinated polynucleotide bind to double stranded polynucleotides known to adopt the Z-conformation. At low and high ionic strength the circular dichroism spectrum of platinated poly(dG-dC).poly(dG- dC) does not resemble that of poly(dG-dC).poly(dG-dC) (B or Z conformation). At low ionic strength, the characteristic 31P nuclear magnetic resonance spectrum of the Z-form is not detected. It appears only at high ionic strength, as a component of a more complex spectrum.

Circular Dichroism↗
PubMed1984

Reaction of cis-diamminedichloroplatinum (II) and DNA in B or Z conformation.

The nature of the adducts and the conformational changes produced in poly(dG-m5dC).poly(dG-m5dC) by cis-diamminedichloroplatinum(II) (cisPt) have been studied. In the reaction of cisPt and B-DNA, the main adduct is bidentate and arises from an intrastrand cross-link between two guanine residues separated by a cytosine. This was deduced from the study of the compounds by t.l.c. after acid hydrolysis of the polymer. The platinated polymer is not digested by S1 nuclease. The antibodies to Z-DNA bind to the platinated polymer with a smaller affinity than to poly (dG-br5dC).poly(dG-br5dC). The c.d. spectrum differs from that of poly(dG-br5dC).poly(dG-br5dC) or poly(dG-m5dC).poly-(dG-m5dC) in Z conformation. It is concluded that the bidentate adduct induces a conformational change from the B form towards a distorted Z form. In the reaction of cisPt and Z-DNA, a monodentate adduct is formed. This adduct stabilizes the Z conformation as shown by c.d. and binding to the anti-Z-DNA antibodies. At room temperature, the second function of the drug can still react with small ligands such as NH4HCO3. By heating, the second function reacts with a guanine residue. A bidentate adduct is formed as in the reaction of cisPt and B-DNA and it induces a transition from the Z form to the distorted Z form.

Animals↗
PubMed1984

Chemically modified nucleic acids as immunodetectable probes in hybridization experiments.

Guanine residues in nucleic acids can be modified by treatment with N-acetoxy-N-2-acetylaminofluorene and its 7-iodo derivative in an in vitro nonenzymatic reaction. The modified nucleic acids (ribo or deoxyribo, single or double stranded) are recognized by specific antibodies. They can be immunoprecipitated or used as probes in hybridization experiments and detected by immunochemical techniques.

Acetoxyacetylaminofluorene↗
PubMed1984

Monoclonal antibodies to DNA modified by the carcinogen N-acetoxy-N-2 acetyl aminofluorene.

BALB/c mice were immunized against acetyl aminofluorene-substituted guanosine (AAF.Guo). Hybridomas were generated from the immune splenocytes fused with the SP2/0.Ag8 cell line. Four monoclonal antibodies (mAb) were selected. Two of them recognize mainly AAF. substituted DNA but also native DNA, while the others (derived from the hybridoma 16) are specific for the modified DNA. Using a solid phase radioimmunoassay, the fine specificity of mAb 16 was examined. The interaction between purified mAb 16 an AAF.DNA is inhibited by either AAF.GMP, AAF.Guo, or AAF.DNA. Moreover this interaction is slightly inhibited by aminofluorene-substituted guanosine (AF.Guo). By control, free AAF, fluorenamine, guanosine, desoxy GMP and native DNA do not compete in the assay. This mAb 16, which specifically recognizes the AAF-nucleotide complex may be a very useful tool to analyze the carcinogenic processes. Such an antibody can also be used for chromosomal localization of genes by AAF-substituted probes.

2-Acetylaminofluorene↗
PubMed1984

Presence of Z-DNA specific antibodies in Crohn's disease, polyradiculoneuritis and amyotrophic lateral sclerosis.

Two modified polynucleotides having the Z-DNA conformation (poly [dG-dC] dien Pt and poly [dG-br5dC] . poly [dG-br5dC]) have been used for determination of antibodies to Z-DNA. Such antibodies were found in sera of patients with systemic lupus erythematosus and with Crohn's disease. They were scarcely observed in polyradiculoneuritis and in amyotrophic lateral sclerosis. In Crohn's disease sera, no antibodies to B-DNA were ever found but presence of two different families of antibodies to Z-DNA was demonstrated.

Adult↗
PubMed1983

Preferential binding of the chemical carcinogen N-hydroxy-2-aminofluorene to B-DNA as compared to Z-DNA.

The reaction between the chemical carcinogen N-hydroxy-2-aminofluorene and poly (dG-dC) . poly (dG-dC) (B-form), poly (dG-m5dC) . poly (dG-m5dC) (B-or Z-form), poly(dG-br5dC) . poly (dG-br5dC) (Z-form) has been studied. The carcinogen binds covalently to B-DNA but does not bind significantly to Z-DNA. These results are discussed as related to the accessibility, the electrostatic potential and the dynamic structure of DNA. The accessibility and the electrostatic potential of DNA do not explain the difference in reactivity of the carcinogen since a related carcinogen N-acetoxy-N-acetyl-2-aminofluorene binds equally well to both B and Z-DNA. On the other hand, poly (dG-dC) . poly(dG-dC) and poly (dG-br5dC) . poly(dG-br5dC), in presence of ethidium bromide binds equally well to N-hydroxy-2-aminofluorene. It is suggested that the very low binding of this carcinogen to Z-DNA as compared to B-DNA is due to differences in the dynamic structures of these two forms of DNA.

Carcinogens↗
PubMed1983

Spectroscopic studies of (m5dC-dG)3: thermal stability of B- and Z-forms.

The hexanucleoside pentaphosphate d(m5CpGpm5CpGpm5CpG) has been studied in solution by ultra-violet absorption, circular dichroism and 31P nuclear magnetic resonance under various experimental conditions. In 0.2 M NaClO4 at low temperature, an hexamer duplex is formed which has a B or B-like conformation. As the salt concentration is increased, a transition from a B-form to the Z-form occurs and is complete in 3 M NaClO4. In 3 M NaClO4, the behavior of the Z double helix is complex as a function of temperature. The variation of the circular dichroism at 295 nm is biphasic. A first transition occurs over a large range of temperature and corresponds to a conformational change due to a non-cooperative intramolecular process. Ultra-violet absorption and 31P nuclear magnetic resonance show that the new conformation arising from a distortion of the backbone is not similar to that observed in low salt conditions (B-form). At high hexanucleotide concentration, aggregates are formed. The second transition is cooperative and corresponds to the melting of a double stranded helix into single strands.

Circular Dichroism↗
PubMed1983

Z-DNA immunoreactivity in fixed metaphase chromosomes of primates.

Antibodies against Z-DNA bind to fixed metaphase chromosomes of man and Cebus albifrons (Platyrrhini, Primate). By indirect immunofluorescence and indirect immunoperoxidase techniques, a heavy staining is detected in some segments of chromosomes of C. albifrons. These segments correspond to R-band-positive heterochromatin, which has a high G + C-base content. Euchromatin of human and Cebus chromosomes show a weak and heterogeneous staining that consistently reproduces an R- and T-banding pattern in both species. Because chromosome homologies previously were demonstrated between these distantly related species by chromosome banding, our results suggest that Z-DNA has been conserved during the course of primate evolution.

Animals↗
PubMed1983

Conformation of oligonucleotides and nucleic acids modified with 2-aminofluorene or 2-acetylaminofluorene.

The first part of this work deals with the thermal stability of oligonucleotides modified with acetylaminofluorene and aminofluorene, respectively. The complementary oligonucleotides d(CGCG), d(CGTACG) and d(AATTGCAATT) have been studied by ultraviolet absorption and circular dichroism. In high salt concentration and at low temperature, the three oligonucleotides form double-stranded helices which have the B-form Substitution of guanine residues in these oligonucleotides by acetylated or deacetylated aminofluorene residues destablizes the B-form and does not induce the transition to the Z-form. The second part of the work deals with the antibodies to Z-DNA. The specificity of these antibodies has been determined by radioimmunoassay. The antibodies react with the Z-form but not with the B-form. Poly(dG-dC).poly(dG-dC) modified by acetylaminofluorene residues is recognized by the antibodies. The antibodies can detect the Z-form in natural DNA as visualized by fluorescent staining of polytene chromosomes from Drosophila melanogaster.

2-Acetylaminofluorene↗
PubMed1982

Interaction between antibodies to Z-form deoxyribonucleic acid and double-stranded polynucleotides.

Antibodies to Z-DNA have been elicited in rabbits immunized with chloro(diethylenetriamine)platinum(II)chloride (Cl2dienPt) modified poly(dG-dC).poly(dG-dC). Under physiological conditions this polynucleotide in which 12% of the bases were substituted is in the Z form. The antibodies are mainly immunoglobulins G as shown by gel filtration of the antiserum and by ultracentrifugation of the antibodies purified on a Sepharose--poly(dG-dC).poly(dG-dC) column. From the quantitative precipitin curve, it is concluded that each binding site of the antibody covers four nucleotide residues. The Z-form DNA-antibody complex is stabilized by electrostatic interactions. There was no interaction between poly(dI-br5dC).poly(dI-br5dC) in the Z form and the antibodies, which strongly suggests that the exocyclic amino group of guanine residues in Z-poly(dG-dC).poly(dG-dC) interacts with the antibody binding site. The modification of poly(dG-dC).poly(dG-dC) by 2-(acetylamino)fluorene residues decreases but does not prevent the binding to the antibodies. It is also shown that the polynucleotide poly(dG-br5dC).poly(dG-br5dC) adopts the Z form over a large range of salt concentration [5 mM tris(hydroxymethyl)aminomethane hydrochloride, pH 7.5, to 3 M NaCl].

Animals↗