Interaction between acridine orange and polyriboadenylic acid

The absorption spectra and circular dichroism of aqueous solutions of acridine orange mixed with polY(riboadenylic acid) [poly(rA)] have been measured for different mixing ratios at acid and neutral pH. The binding ratio of dye to poly(rA) has been determined by equilibrium dialysis. At acid pH where poly(rA) is in a double-stranded helix, monomeric dye molecules are intercalated between base pairs, first sparsely and then at neighbouring sites with mutual coupling, as the nucleotide-to-dye mixing ratio decreases. In the presence of excess dye, dimeric dye molecules of antiparallel type are bound to phosphate groups electrostatically and stack together to form linear sequences along a poly(rA) chain. At neutral pH where poly(rA) is single-stranded, isolated intercalation of monomeric dye molecules can occur in the helical parts. At intermediate mixing ratios, half-intercalated dimeric dye molecules are bound to adjacent sites and electronically coupled, inducing characteristic circular dichroism. In the presence of higher amounts of dye, external stacking of dimeric dye molecules of antiparallel type occurs along a poly(rA) chain. The binding of dye cations is suppressed to some degree at acid pH compared to that at neutral pH, owing to the repulsion exerted by protonated adenine bases.     

Kinetic studies of interaction between acridine orange and DNA

The interaction between acridine orange (AO) and deoxyribonucleic acid (DNA) was studied by the stopped-flow method. The spectral change of AO due to interaction with DNA was followed over the wavelength range 350–600 nm at various concentration ratios of DNA phosphate to dye. The spectral change observed by the stopped-flow method was found distinctly different from that, during the dead-time, leading to a conclusion that the binding of AO to the outside of DNA occurs much faster than the intercalation into base pairs of DNA. The dependence of the rate of reaction on the reactant concentration and on the salt, concentration of the solution was also studied. The results are consistent with the mechanism that the intercalation proceeds via the outside bound state.     

The comparative analysis of interaction between acridine orange and DNA-containing systems]

The interaction between acridine orange (AO) and diluted and concentrated solutions of DNA, DNP systems and chromatin suspension at the physiologic ionic strength was investigated. The effect of AO on DNP systems was also investigated. It was shown that highest possible number of AO molecules bound to DNA made up 70% of the total number of nucleotides. The model of AO binding to DNA is proposed and used for calculation of constants of stronger and weaker AO-binding capacities equal to 6-10(6) M-1 and 1,7-10(5) M-1, respectively. The AO-DNA binding constants in DNP-complex are five as low. The primary number of binding sites in chromatin suspension made up 10% of the corresponding sites in DNA and increased as AO was adsorbed. AO induced the supercontraction of oriented DNP systems at the physiologic ionic strength and the appearance of the low-temperature melting hump.     

Molecular Complexes of acridine orange and nucleosides

Summary The addition of various nucleosides to the aqueous AO solution brings about the red shift of the absorption band of AO monomer and the enhancement of the AO fluorescence emission. These phenomena are attributable to the formation of a kind of molecular complex between AO monomer and nucleoside.The absorption and fluorescence characteristics and their thermal behaviours enable us to determine the association constant and the binding energy. The binding energy of AO with purines is larger than that with pyrimidines, and the association constant between AO and the deoxyribonucleoside is larger than that between AO and the ribonucleoside. For the molecular complexes dealt with, the face-to-face arrangement of AO and nucleoside, linking of AO with sugar by hydrogen bridge, may be more preferential than the side-by-side arrangement with the direct linkage between AO and nucleic acid base by hydrogen bonding. The Van der Waals-London interactions may be one of the essential factors for the binding in these molecular complexes.The association constant and the binding energy for AO-DNA and -RNA systems were also determined. The magnitude of these quantities seems to reflect the difference in the structure of these nucleic acids. The rather open structure of RNA compared with DNA is in favour of affinity with AO and gives the larger association constant than that for AO-DNA. The binding energy is somewhat larger for AO-DNA complex than for AO-RNA complex, probably due to the structural difference of the base arrangement; the stacked base pairs for DNA and the stacked bases for RNA.This may explain the selective degradation [12] of guanine photo-sensitized by dyes either in the free state or when incorporated to DNA or RNA, as discussed elsewhere.     

Apolipoprotein E promotes astrocyte colocalization and degradation of deposited amyloid-beta peptides

We have previously shown that apolipoprotein E (Apoe) promotes the formation of amyloid in brain and that astrocyte-specific expression of APOE markedly affects the deposition of amyloid-beta peptides (Abeta) in a mouse model of Alzheimer disease. Given the capacity of astrocytes to degrade Abeta, we investigated the potential role of Apoe in this astrocyte-mediated degradation. In contrast to cultured adult wild-type mouse astrocytes, adult Apoe(-/-) astrocytes do not degrade Abeta present in Abeta plaque-bearing brain sections in vitro. Coincubation with antibodies to either Apoe or Abeta, or with RAP, an antagonist of the low-density lipoprotein receptor family, effectively blocks Abeta degradation by astrocytes. Phase-contrast and confocal microscopy show that Apoe(-/-) astrocytes do not respond to or internalize Abeta deposits to the same extent as do wild-type astrocytes. Thus, Apoe seems to be important in the degradation and clearance of deposited Abeta species by astrocytes, a process that may be impaired in Alzheimer disease.     

Study on the interaction between cannabinol and DNA using acridine orange as a fluorescence probe

The interaction between cannabinol (CBN) and herring‐sperm deoxyribonucleic acid was investigated by using acridine orange as a fluorescence probe in this work. UV‐Vis spectroscopy, fluorescence spectroscopy, and DNA melting techniques were used. The fluorescence of DNA acridine orange was quenched by CBN. The results indicated that CBN can bind to DNA. The binding constant for the CBN and herring‐sperm deoxyribonucleic acid was obtained at 3 temperatures, respectively. Results of molecular docking corroborated the experimental results obtained from spectroscopic investigations. The influence of ionic strength on the fluorescence properties was also investigated. The thermodynamic results indicated that hydrophobic interaction played a major role in the binding between CBN and DNA.     

Fluorescence of acridine orange in the composition of blood and tissues

The interaction of acridine orange with blood albumins and tissue cells from different organs of white mouse has been studied by the spectral luminescence method. It was shown that acridine orange, by penetrating cells or organelles, is able to intercalate between base pairs in the DNA molecule. It was found that the application of acridine orange as a fluorescent probe can influence the metabolic activity of organs.     

Molecular mechanical studies of proflavine and acridine orange intercalation.

Previous workers have reported that proflavine and acridine orange form various structurally different complexes with the dinucleoside phosphates rCpG and dCpG, with uniform C3'-endo and mixed C3'-endo (3'-5') C2'-endo sugar puckers being observed. We present theoretical calculations, based on the method of molecular mechanics, which support the experimental observations. The results suggest that the mixed C3'-edo (3'-5') C2'-endo pucker conformation isi intrinsically more stable than the uniform C3'-endo conformation, but that the additional stabilisation gained from specific, hydrogen bonding, interactions between nucleic acid and solvent, or intramolecularly within the nucleic acid, can lead to the adoption of the latter conformation, or of variants between the two. The role played by hydrogen bonding between amino-groups and nucleic acid phosphate appears more subtle than previously supposed.