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Biomedical subjects

M Leng

Publications and source records attributed to M Leng.

At least 127 records · Page 7Linked to original sources
PubMed1982

Non-random binding of N-acetoxy-N-2-acetylamino-fluorene to chromatin subunits as visualized by immunoelectron microscopy.

The influence of chromatin structure on the accessibility of DNA to the model ultimate carcinogen N-acetoxy-N-2-acetylaminofluorene (N-Aco-AAF) was investigated by means of an immunoelectron microscopic technique developed recently. An homogeneous population of core particles or trinucleosomes from chicken erythrocytes, was submitted to electrophilic attack by N-Aco-AAF. After DNA isolation, N-2-acetylaminofluorene (AAF) binding sites were mapped upon the DNA fragments using specific antibodies as a probe. Our results indicate a non-random binding of AAF along the DNA. Our data support the results of previous studies showing a preferential binding on the linker region.

2-Acetylaminofluorene↗
PubMed1982

The B reversible Z transition of poly(dI-br5dC).poly(dI-br5dC). A quantitative description of the Z form dynamic structure.

The study of poly(dI-br5dC).poly(dI-br5dC) films by infrared spectroscopy shows that in low salt concentration, the conformation of this polynucleotide belongs to the B-family and in high salt concentration to the Z-family. 31P nuclear magnetic resonance and circular dichroism confirm the existence of these two forms. By circular dichroism and ultraviolet absorption, it is shown that the equilibrium constant of the B reversible Z transition depends upon temperature. The deuteration rates of exchangeable protons involved in hydrogen bonds between base pairs were deduced from the changes in absorbance near 1700 cm-1. In the B-form, one class of protons is measured with an exchange half-time of 20 minutes. In the Z-form, two classes of protons are measured with very different exchange half-times, the exchange half-time of the slow protons being of the order of 850 minutes. By comparison of these results with those previously obtained for poly(dG-dC).poly(dG-dC), these very slow protons of these two Z-polynucleotides are identified as the cytosine amino protons. A quantitative description of the dynamic structure of the Z-form is presented.

Circular Dichroism↗
PubMed1982

Polynucleotide helix geometry and stability. Spectroscopic, antigenic and interferon-inducing properties of deoxyribose-, ribose-, or 2'-deoxy-2'-fluororibose-containing duplexes of poly(inosinic acid) . poly(cytidylic acid).

Circular dichroism, absorbance temperature profiles, antigenic properties, and interferon-inducing capacity of the nine double-stranded complexes between poly(inosinic acid) and poly(cytidylic acid) [(rI)n . (rC)n] and their deoxy- and 2'-deoxy-2'-fluoro-analogues were studied. The complexes containing only ribose or 2'-fluororibose chains showed similar CD spectra and thermal stabilities. Anti-(rI)n . (rC)n antibodies were well recognized by the duplexes containing 2'-fluororibose in either one strand. These two duplexes were also efficient interferon inducers. Presence of fluororibose in both strands decreased the affinity of anti-(rI)n . (rC)n antibodies slightly and abolished interferon-inducing activity. All polydeoxyriboside-containing complexes showed CD spectra significantly different from the previous group; they showed also 40- to 100-times lower affinity for the anti-(rI)n . (rC)n antibodies, and did not induce interferon. It is concluded that the structure of (rI)n . (rC)n, an A-type helix, is little perturbed by substitution of one or both strands by 2'-fluororibose. Substitution by deoxyribose in either strand considerably changes the structure of the helices. The hybrids containing poly(deoxycytidylic acid) retain at least some of the structural features of the B-type helix poly(deoxyinosinic acid) . poly(deoxycytidylic acid).

Animals↗
PubMed1982

Visualization of Z sequences in form V of pBR322 by immuno-electron microscopy.

Form V DNA has been prepared from pBR322 DNA by annealing covalently closed complementary single strands. Specific rabbit antibodies to Z-DNA were shown by radioimmunoassay and electron microscopy to react with form V DNA of pBR322. The bound antibodies were visualized either directly (on synthetic polynucleotides in Z-form), or after reaction with goat anti-rabbit immunoglobulin labeled with ferritin (on form V DNA).

Antigen-Antibody Complex↗
PubMed1982

Comparison of poly(dG-dC).poly(dG-dC) conformations in oriented films and in solution.

The structures of B and Z forms of poly(dG-dC).poly(dG-dC) in oriented hydrated films have been investigated by infrared spectroscopy. First, the infrared linear dichroism spectrum of poly(dG-dC).poly(dG-dC) in B form (high relative humidity and 2 M Na+) was recorded. The spectrum of the Z form was recorded at a lower relative humidity and higher sodium content (4 M). The experimental conditions were similar to those used in x-ray diffraction studies of left-handed poly(dG-dC).poly(dG-dC) fibers. A qualitative agreement was found between the calculated values of the angles characteristic of the orientation of PO-2 groups with respect to the helical axis in the ZI form and the experimental values. The infrared spectra of B and Z form and the experimental values. The infrared spectra of B and Z forms show some significant differences in H2O and 2H2O. The deuteration rates of exchangeable protons involved in hydrogen bonds between guanine and cytosine residues were deduced from the changes in absorbance near 1700 cm-1. In the B form, the exchange half-time is of the order of 20 min. In the Z form, the exchange half-time of some protons is very slow, of the order of 24 hr. Because of the similarity between these values and those previously reported for the high-salt and low-salt form of poly(dG-dC).poly(dG-dC) in solution, we conclude that the high-salt form of poly(dG-dC).poly(dG-dC) in solution belongs to the Z family.

Kinetics↗
PubMed1982

Detection of N-hydroxy-2-acetylaminofluorene-DNA adducts in rat liver measured by radioimmunoassay.

Antibodies to imidazole ring opened derivatives of alkali treated N-(guanosin-8-yl)-2-aminofluorene (1-[6-(2,5-diamino-4-oxopyrimidinyl-N6-riboside)]-3-(2-fluorenyl)urea were elicited in rabbits by immunization with a conjugate between the ring-opened derivative and bovine serum albumin. The specificity of the antibodies was studied by radioimmunoassay. These antibodies and antibodies to N-(guanosin-8-yl)-N-acetyl-2-aminofluorene were used to titrate the adducts formed in liver DNA of rats treated with N-hydroxy-2-acetylaminofluorene. The ring-opened derivatives represent approximately 10% of the dGuo-C8-adducts.

2-Acetylaminofluorene↗
PubMed1981

The B goes to Z transition of poly(dG-dC) . poly(dG-dC) modified by some platinum derivatives.

Poly(dG-dC) . poly(dG-dC) was modified by chlorodiethylenetriamino platinum (II) chloride, cis-dichlorodiammine platinum (II) and trans-dichlorodiammine platinum (II), respectively. The conformation of these modified poly(dG-dC) . poly(dG-dC) was studied by circular dichroism. In 4 M Na+, the circular dichroism spectra of poly(dG-dC)dien-Pt (0 less than or equal to rb less than or equal to 0.2) are similar (rb is the amount of bound platinum per base). It is concluded that the conformation of these polymers belongs to the Z-family. Dien-Pt complexes stabilize the Z-form. The midpoint of the Z goes to B transition of poly(dG-dC)dien-Pt(0.12) is at 0.2 M NaCl. Moreover another B goes to Z transition is observed at lower salt concentration (midpoint at 6 mM NaCl). In 1 mM phosphate buffer, the stability of Z-poly(dG-dC)dien-Pt(0.12) is greatly affected by the presence of small amounts of EDTA. Poly(dG-dC) . poly(dG-dC) modified by cis-Pt and trans-Pt complexes do not adopt the Z-form even in high salt concentration.

Circular Dichroism↗
PubMed1981

Conformational changes of poly(dG-dC) . poly(dG-dC) modified by the carcinogen N-acetoxy-N-acetyl-2-aminofluorene.

Poly (dG-dC) . poly(dG-dC) was modified by the reaction with N-acetoxy-N-acetyl-2-aminofluorene. The conformations of poly(dG-dC) . poly(dG-dC) and of poly d(G-C)AAF were studied by circular dichroism under various experimental conditions. In 95% ethanol, the two polynucleotides adopt the A-form. In 3.9 M LiCl, the transition B-form-C-form is observed with poly(dG-dC) . poly (dG-dC) but not with poly d(G-C)AAF. In 1 mM phosphate buffer, poly d(G-C)AAF behaves as a mixture of B- and Z-form, the relative percentages depending upon the amounts of modified bases. The percentage of Z-form is decreased by addition of EDTA and is increased by addition of Mg++. Spermine favors the Z-form in modified and unmodified polynucleotides. No defect in the double helix of poly d(G-C)AAF is detected by SI endonuclease.

2-Acetylaminofluorene↗
PubMed1981

Synthesis and structural studies of a self-complementary decadeoxynucleotide d(AATTGCAATT). I.-Synthesis and chemical characterization of the decanucleotide.

The synthesis of the self-complementary decadeoxynucleotide d(AATTGCAATT) is described. The phosphotriester method has been used with several modifications. Protected nucleotides have been prepared in a one-step reaction involving a new monofunctional phosphorylating agent: p-chlorophenyl-beta-cyanoethyl phosphate. Triethylammonium salts of mononucleoside 3'-phosphodiesters were obtained either by decyanoethylation of the triesters or, in the case of thymine, by a one-step reaction starting from 5'-0-methoxytritylthymidine and the mixture pyridine-para-chlorophenyl-methyl-phosphorobromidate. The usual coupling reactions were then used to prepare the decadeoxynucleotide in large quantities.

Chemical Phenomena↗
PubMed1981

Immunochemical studies of DNA modified by cis-dichlorodiammineplatinum(II) in vivo and in vitro.

Two rabbits were immunized with native DNA modified in vitro by cis-dichlorodiammineplatinum(II) (cis-Pt). The interactions between the antiserum and several natural and synthetic nucleic acids were studied primarily by radioimmunoassays. Native DNA's modified by platinum compounds with labile groups in the cis position are recognized by the antiserum. No cross-reaction is found with native DNA's substituted by other platinum compounds [trans-dichlorodiammineplatinum(II), cis-diamminotetrachloroplatinum(IV), and chlorodiethylenetriamminoplatinum(II)] and with natural and synthetic modified polyribonucleotides. cis-Pt-modified oligodeoxyribonucleotides and enzymatically hydrolyzed cis-Pt-modified native DNA do not bind to the antiserum. cis-Pt-modified double-stranded synthetic polydeoxyribonucleotides are either hardly recognized or not recognized at all. The antiserum recognized a modified double-stranded helix in DNA which is not formed in several modified synthetic DNA's and RNA's. At least two different antigenic determinants are present in cis-Pt-modified DNA at a ratio of cis-Pt to bases equal to 0.05. Finally, the antiserum does not react with in vivo cis-Pt-modified DNA.

Animals↗
PubMed1981

Structural modification and protein recognition of DNA modified by N-2-fluorenylacetamide, its 7-iodo derivative, and by N-2-fluorenamine.

Several experimental approaches were used to compare the structural modifications introduced by the binding to DNA of N-hydroxy-N-2-fluorenamine and of N-acetoxy-N-2-fluorenylacetamide and its 7-iodo derivative. In the three binding reactions, the major part of the substitution occurred at C-8 of guanine. Formaldehyde unwinding, hydrolysis by endonuclease S(1), linear electric dichroism, circular dichroism, use of antibodies, unwinding of covalently closed circular DNA, and binding of tripeptide were thus successively examined. Most of the techniques showed marked differences between the different modified DNA's. However, some experiments failed to show discrimination between the induced structural alterations. These specific points are discussed. On the basis of all the available experimental evidence and after examination of the Cory-Pauling-Koltun molecular model, we proposed three models of DNA binding at the C-8 of the guanine residue with 1) the 7-iodo derivative (outside binding) 2), N-acetoxy-N-2-fluorenylacetamide (insertion-denaturation) and 3) N-hydroxy-N-2-fluorenamine (insertion without denaturation).

2-Acetylaminofluorene↗
PubMed1980

Antibodies to N-(guanosin-8-yl)-2-aminofluorene.

Antibodies to Guo-AF were elicited in rabbits by immunization with bovine serum albumin -Guo-AF conjugate. The antibodies were purified by affinity chromatography. The affinity of the antibodies towards several ligands was studied by radioimmunoassays. The antibodies recognize Gua-AAF and Guo-AF (K(Guo-AF)/K(Guo-AAF) congruent to 25). The circular dichroism of Guo-AF as a function of pH is reported.

Animals↗
PubMed1980

Conformation of poly(dG-dC) . poly(dG-dC) modified by the carcinogens N-acetoxy-N-acetyl-2-aminofluorene and N-hydroxy-N-2-aminofluorene.

Poly(dG-dC) . poly(dG-dC) was modified by reaction with N-acetoxy-N-acetyl-2-aminofluorene (N-AcO-AAF). Two samples with 6.6% and 8.5% modified bases were prepared. The modified bases are randomly distributed along the polymer chain, as deduced from competition experiments between antibodies against N-2-(guanosin-8-yl)-acetylaminofluorene, modified poly(dG-dC) . poly(dG-dC), and modified DNAs. Circular dichroism studies show that poly(dG-dC) . poly(dG-dC) modified by N-AcO-AAF is much more sensitive to the addition of alcohol than poly(dG-dC) . poly(dG-dC). In about 50% (vol/vol) alcohol, both polynucleotides have the same conformation, which is the Z form or a Z-like form. Moreover, in low salt and in the absence of alcohol, poly(dG-dC) . poly(dG-dC) modified by N-AcO-AAF is partially in the Z form. Poly(dG-dC) . poly(dG-dC) modified by N-hydroxy-N-2-aminofluorene can also adopt the Z form, but the transition is induced at a higher percentage than that of poly(dG-dC) . poly(dG-dC) modified by N-AcO-AAF. In low salt and in the absence of alcohol, no Z form was detected in poly(dG-dC) . poly(dG-dC) modified by N-hydroxy-N-2-aminofluorene.

2-Acetylaminofluorene↗