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Biomedical subjects

M Leng

Publications and source records attributed to M Leng.

At least 163 records · Page 9Linked to original sources
PubMed1976

Heterogeneity of antibodies to adenosine 5'-monophosphate.

Antibodies to adenosine 5'-monophosphate were produced in rabbits by injecting a conjugate of the nucleotide (oxidized with periodate) with bovine serum albumin. AMP-specific antibodies were isolated by affinity chromatography. The antiserum was first applied on oligoadenylic acids-agarose column and then the unbound proteins on a morpholine derivative of AMP-agarose column. The antibodies purified on these two columns interact differently with AMP derivatives as shown by immunodiffusion. These results are confirmed by the values of the binding constants of the complexes Fab fragments- AMP and AMP derivatives. The study of Fab fragments -- C(8)-substituted AMP derivatives complexes suggest a syn conformation for the bound nucleotide. Thermodynamic parameters for the Fab fragments-AMP complexes have been determined (deltaHdegrees = --13 kcal/mol and deltaSdegrees = --15 cal - degree-1 - mol-1).

Adenosine Monophosphate↗
PubMed1976

Binding isotherms and the interaction between proflavin and a DNA of high G-C content.

Binding isotherms corresponding to several situations of ligand binding to a linear polymer are calculated, including cases of cooperativity or anticooperativity between the bound ligand states, multiple binding modes that are competitive or non competitive, and possible exclusive of an arbitrary number of adjacent sites upon occupancy of a site by a single ligand. The sequence generating function method of Lifson and Bradley is used, requiring the assumption that no end effects are involved. The case of strong binding of the dye proflavin to a DNA of high G-C content, that of M. lysodeikticus, is considered in detail, and a single model capable of reconciling the available kinetic and equilibrium data on this system, involving two competing binding modes, is discussed.

Acridines↗
PubMed1976

Recognition of polynucleotides by antibodies to poly(I), poly(C).

The binding of anti poly(I). poly (C) Fab fragments to double or triple stranded polynucletides has been studied by fluorescence. Association constants were deduced from competition experiments. The comparison of the association constants leads to the conclusion that several atoms of the base residues do not interact with the amino acid residues of the binding site of Fab fragment while the hydroxyl groups of furanose rings interact. These results suggest that the Fab fragments do not bind to the major groove of the double stranded polynucleotides. An interaction between the C(2)O group of pyrimidine residues and Fab fragments cannot be excluded. Circular dichroism of poly(I). poly(C) or poly(I). poly(br5C)-Fab fragments complexes are very different from the circular dichroism of free polynucleotides which suggests a deformation of the polynucleotides bound to the Fab fragments.

Antigen-Antibody Complex↗
PubMed1975

Antibodies to adenosine 5'-monophosphate: purification and specificity.

Antibodies to adenosine-5'-monophosphate were produced in rabbits by injecting a conjugate of the nucleotide (oxidized with periodate) with bovine serum albumin. Nucleotide-specific antibodies were isolated by affinity chromatography on oligoadenylic acids/agarose column. Pure immunoglobulin G antibodies were obtained by gel filtration on Sephadex G-200. These antibodies, as analyzed by double diffusion react with adenosine 5'-monophosphate--bovine serum albumin, slightly with inosine-5'-monophosphate conjugate and not at all with the other nucleotide conjugates. The association constants for adenosine-5'-monophosphate--antibody complex formation obtained by dialysis equilibrium and fluorescence measurements, are in good agreement. This latter technique was used to study on one hand the influence of temperture and salt on complex formation, on the other hand the interaction of the antibodies with AMP derivatives. The phosphate group, the ribose and the base are recognized by the antibody, but the C-8 atom of adenine residues is not directly involved in the binding.

Adenosine Monophosphate↗
PubMed1975

Effect of DNA base composition on the intercalation of proflavine. A kinetic study.

The effect of DNA base composition on the kinetics of the association between DNA and proflavine has been investigated using the temperature jump relaxation method. It is found that, regardless of the G + C base composition the results fit a two step mechanism, the second of which exhibits characteristics of intercalation of proflavine into DNA. However, they two equilibrium constants corresponding to these steps, KI and KII, depend on the nature of the DNAs. The constant KI is found to be an order of magnitude greater for M. lysodeikticus DNA (72% G + C) than for calf thymus DNA (48% G + C). Increasing G-C content thus appears to favor the intermediate non-intercalated complex of proflavine with DNA. Methylation of M. lysodeikticus DNA with dimethyl sulfate, preferentially yielding N7 methyl guanine as the modified base, again leads to an apparent two step mechanism, with the value of KI unchanged with respect to untreated DNA, while the affinity of proflavine for the intercalated complex measured by the value of KII increases for methylated DNA.

Acridines↗