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Biomedical subjects

M Leng

Publications and source records attributed to M Leng.

At least 145 records · Page 8Linked to original sources
PubMed1980

Antibodies to N-hydroxy-2-aminofluorene modified DNA as probes in the study of DNA reacted with derivatives of 2-acetylaminofluorene.

Antibodies were elicited in rabbits immunized with a mixture of methylated bovine serum albumin and N-hydroxy-2-aminofluorene reacted DNA (DNA-AF). These antibodies were used in competition radioimmunoassays (RIA) with [3H]DNA-AF as radioactive antigen and different N-acetoxy-2-acetylaminofluorene (N-AcO-AAF) and N-hydroxy-2aminofluorene (N-OH-AF) reacted DNAs, deoxyguanosine, dGMP, dGpA and dApG as inhibitors. Based on the results of RIA it is concluded that the binding sites of the two residues, -AF and -AAF, to guanosine in DNA, are essentially the same. Moreover, the same sites seem to be reactive also in the direct reaction of N-AcO-AAF with dGMP. Circular dichroism measurements of modified DNA confirm the RIA results.

Acetoxyacetylaminofluorene↗
PubMed1979

Alkaline stability of guanosine and some of its derivatives modified by the carcinogen N-acetoxyacetylaminofluorene.

The alkaline treatment of Guo, dGuo, dGMP and denatured DNA modified by N-acetoxyacetylaminofluorene (N-AcO-AAF) was performed in 0.1 M NaOH at 40 degrees C. The kinetics of the reaction were followed by ultraviolet absorption and by chromatographic methods and were found different for the four products under study. Circular dichroism spectra show differences in the environment of acetylaminofluorene residue in these products. The alkaline treatment of Guo-AAF (and dGuo-AAF) leads to the formation of three products. These products were separated by thin layer chromatography and by HPLC and were characterized by spectroscopic methods. One is the already known unstable Guo-AF (and respectively dGuo-AF) (1). The other two products are relatively stable products of the transformation of Guo-AF (or dGuo-AF). These last ones present almost identical ultraviolet absorption spectra, but very different circular dichroism spectra.

2-Acetylaminofluorene↗
PubMed1979

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

Rabbits were immunized with native DNA modified by the carcinogen N-acetoxy-N-acetyl-2-aminofluorene. The interactions between the purified antibodies to nDNA-AAF (or the Fab fragments) and several ligands have been studied. By radioimmunoassay, nDNA-AAF, dDNA-AAF, and GMP-AAF were found to bind to the antibodies with about the same affinity. GMP-AF interacts slightly less, and GMP and N-OH-AAF do not interact. The values of the association constants deduced from fluorescence measurements for the binding of the Fab fragments to nDNA-AAF, dDNA-AAF, and GMP-AAF, in 50 mM NaCl, pH 7.5, are of the same order of magnitude. The values of the association constants with nDNA-AAF and dDNA-AAF depend upon salt concentration. From this variation; it is deduced that 1-1.5 phosphate groups interact by charge--charge interactions with the Fab fragments. The absorption and circular dischroism spectra of GMP-AAF, nDNA-AAF, and dDNA-AAF bound to the Fab fragments show that the Fab fragments induce similar perturbation to the three ligands. These results lead to the conclusion that the immunodeterminant group is the dGMP-AAF residue.

Acetoxyacetylaminofluorene↗
PubMed1979

Electron microscopic visualization of N-acetoxy-N-2-acetylaminofluorene binding sites in ColE1 DNA by means of specific antibodies.

ColE1 DNA has been allowed to react in vitro with N-acetoxy-N-2-[14C]acetylaminofluorene in the range of 0-15 N-2-[14C]acetylaminofluorene residues bound per molecule of DNA, at the C8 of guanine residues. Purified rabbit antibodies to both N-2-(guanosine-8-yl)-acetylaminofluorene and native DNA that had reacted with N-acetoxy-N-2-acetylaminofluorene were shown by electron microscopy to recognize specifically the acetylaminofluorene-modified ColE1 DNA. The antibodies bound to DNA were visualized either per se or after reaction with goat anti-rabbit immunoglobulins coupled with ferritin. There was a linear relationship between the average number of antibodies bound per DNA molecule and the number of N-2-(deoxyguanosine-8yl)-acetylaminofluorene residues per DNA molecule. The slope of this straight line was equal to 0.4. Due to the bivalence of the immunoglobulins one would expect a value of 0.5; we actually observed an important fraction of the bound antibodies crosslinking two parts of the same (or of another) DNA molecule.

2-Acetylaminofluorene↗
PubMed1979

Reactivity of antibodies to guanosine modified by the carcinogen N-acetoxy-N-2-acetylaminofluorene.

N-(guanosin-8-yl) acetylaminofluorene (Guo-AAF) was prepared by the reaction of N-acetoxy-N-2-acetylaminofluorene (AAAF) and guanosine. Antibodies to Guo-AAF were elicited in rabbits by immunization with bovine serum albumin-Guo-AAF conjugate. The antibodies were purified by affinity chromatography on a Sepharose-Guo-AAF column. The reactivity of these antibodies towards several ligands was studied by radioimmunoassay. The antibodies have the same affinity for double stranded DNA-AAF and single stranded DNA-AAF. Thus the geometry of the regions of DNA substituted by AAF residues is the same in native and denatured DNA. The affinity of the antibodies is smaller for DNA-AAF than for Guo-AAF. This can be due in part to the stacking of AAF residues with the adjacent bases as shown by the study of the interactions between the antibodies and AAF-oligonucleotides. The circular dichroism spectra of AAF-oligonucleotides bound to the antibodies are reported.

Acetoxyacetylaminofluorene↗
PubMed1979

Conformational changes induced in DNA by in vitro reaction with N-hydroxy-N-2-aminofluorene.

The conformation of DNA modified in vitro by the covalent binding of N-OH-AF was investigated by ultraviolet absorbance, circular dichroism and by radioimmunoassay using specific antibodies against Guo-AAF and nDNA-AAF. The results obtained by both physico-chemical and immunological methods are in agreement with a model involving destabilized regions in the double helical DNA around the carcinogen molecule in which, however, the -AF residues are stacked to the adjacent nucleotides. The RIA results show that the -AF residues are less accessible to antibodies in native than in denatured DNA-AF and thus suggest -AF residues partially buried in the interior of the DNA helix. The present model is compared to the one existing for DNA modified by reaction with N-AcO-AAF (DNA-AAF) (1,2).

Animals↗
PubMed1978

Further studies on the interaction between polynucleotides and antibodies to poly(inosinic acid). poly(cytidylic acid).

Interactions between antibodies to poly(inosinic acid).poly(cytidylic acid) [poly(I).poly(C)] (or Fab fragments) and double-stranded polynucleotides have been studied by several techniques. In quantitative precipitation tests, the amounts of precipitated antibodies depend upon salt concentration. This effect of salt is reversible. From the comparison of the association constants (deduced from fluorescence measurements) for the binding of Fab fragments to several polynucleotides, a direct interaction between atoms or groups of the bases, which can be involved in hydrogen bonds, can be excluded. The complexes between poly(I).poly(C) and Fab fragments interact with ethidium bromide. The association constants for the binding of ethidium bromide to poly(I).poly(C) and to poly(I).poly(C)-Fab fragments complexes are about the same, but Fab fragments reduce the number of base pairs available to ethidium bromide binding. At saturation of poly(I).poly(C) by Fab fragments, the number of binding sites of ethidium bromide is only reduced by a factor of two. It is concluded that all the nucleotide residues covered by the Fab fragment binding site do not interact with the amino acid residues. Circular dichroism studies of the complexes between Fab fragments and polynucleotides are in favor of some conformational change of the polynucleotides.

Antibodies↗
PubMed1977

Purification and specificity of antibodies to adenosine.

Antibodies to adenosine were elicited in rabbits by immunization with bovine serum albumin-adenosine conjugate. The antibodies were purified and fractionated on two affinity columns (Sepharose-oligo(A) and Sepharose-AMP). Two families of antibodies have been obtained. The antibodies purified on the Sepharose-oligo(A) column react with poly(A) while those purified on the Sepharose-AMP column do not, as shown by gel diffusion. The association constants for the binding of Fab fragments or IgG purified on the Sepharose-oligo(A) column and several haptens were deduced from dialysis equilibrium, fluorescence quenching and displacement of AMP-fluorescein conjugate. The antibodies mainly recognize adenine, and the ribose or the phosphate group of (or AMP derivatives) do not play a critical role in the interaction. Thermodynamic parameters for adenosine-Fab fragments complexes have been determined deltaH degrees = 16 kcal/mole and deltaS degrees = - 15 cal. degree-1 mole-1. Circular dichroism studies indicate that about three nucleotide residues penetrate the binding site of Fab fragments.

Adenosine↗
PubMed1977

Purification and specificity of antibodies to inosine 5'-monophosphate.

Antibodies to inosine 5'-monophosphate elicited in rabbits by immunization with a conjugate of IMP (oxidized with periodate) and bovine serum albumin have been purified by affinity chromatography. By the use of two affinity columns, Sepharose-IMP and Sepharose-oligo(I), the antibodies have been fractionated into three fractions. By gel diffusion, the three fractions were found to react with the conjugates of bovine serum albumin and IMP, GMP and AMP respectively. The association constants for the binding of the Fab fragments purified on the Sepharose-oligo(I) column and several haptens have been deduced from fluorescence experiments. It is shown that the base and the phosphate group play an important part in the binding of IMP to Fab fragments. No reaction has been found between the antibodies and poly(I).poly(C) by gel diffusion. However, the antibodies interact with poly(I).poly(C) since they decrease the thermal stability of poly(I).poly(C).

Animals↗
PubMed1977

Circular dichroism study of polyriboxanthylic acid.

We report in the present paper the circular dichroism spectra of poly(X) at different pH and temperature values. The spectra are characteristic of three stable forms of poly(x) in the pH range of protonation of xanthosine. An electrostatic barrier is proposed to account for the hysteresis and metastability observed in a certain pH range. Some results on oligo(X) at basic pH are also presented. Poly(X) at basic pH is investigated also by hydrodynamic techniques.

Chemical Phenomena↗
PubMed1977

[Ureteric lesions in childhood (author's transl)].

Diagnosis in these cases is particularly difficult. By early intravenous pyelography the site of the injury can be located and presence and function of the contralateral kidney be proved.

Abdominal Injuries↗
PubMed1976

[Specificity of anti-ApA antibodies].

Antibodies to ApA elicited in Rabbits by immunization with bovine serum albumin-ApA conjugate have been purified by affinity chromatography. These purified antibodies react with bovine serum albumin-AMP, 8 bromo AMP, ApA conjugates as shown by gel diffusion. The association constants for the binding of antibodies and several haptens were deduced from dialysis equilibrium. The number of bound hapten molecules per antibody binding site depends upon the nature of the hapten.

Adenine Nucleotides↗