Optical studies of complexes of quinacrine with DNA and chromatin: implications for the fluorescence of cytological chromosome preparations

The fluorescence and circular dichroism of quinacrine complexed with nucleic acids and chromatin were measured to estimate the relative magnitudes of factors influencing the fluorescence banding patterns of chromosomes stained with quinacrine or quinacrine mustard. DNA base composition can influence quinacrine fluorescence in at least two ways. The major effect, evident at low ratios of quinacrine to DNA, is a quenching of dye fluorescence, correlating with G-C composition. This may occur largely prior to relaxation of excited dye molecules. At higher dye/DNA saturations, which might exist in cytological chromosome preparations stained with high concentrations of quinacrine, energy transfer between dye molecules converts dyes bound near G-C base pairs into energy sinks. In contrast to its influence on quinacrine fluorescence, DNA base composition has very little effect on either quinacrine binding affinity or the circular dichroism of bound quinacrine molecules. The synthetic polynucleotides poly(dA-dT) and poly(dA)-poly(dT) have a similar effect on quinacrine fluorescence, but differ markedly in their affinity for quinacrine and in the circular dichroism changes associated with quinacrine binding. Quinacrine fluorescence intensity and lifetime are slightly less when bound to calf thymus chromatin than when bound to calf thymus DNA, and minor differences in circular dichroism between these complexes are observed. Chromosomal proteins probably affect the fluorescence of chromosomes stained with quinacrine, although this effect appears to be much less than that due to variations in DNA base composition. The fluorescence of cytological chromosome preparations may also be influenced by fixation effects and macroscopic variations in chromosome coiling.     

Quinacrine: Spectroscopic properties and interactions with polynucleotides

The acridine dye quinacrine and its interactions with calf thymus DNA, poly(dA-dT) · poly (dA-dT), and poly (dG-dC) · poly(dG-dC) were studied by light absorption, linear dichroism, and fluorescence spectroscopy. The transition moments of quinacrine give rise to absorption bands polarized along the short axis (400–480-nm band), and the long axis (345-nm and 290-nm bands) of the molecule, respectively. Linear dichroism studies show that quinacrine intercalates into calf thymus DNA as well as into the polynucleotides, displaying fairly homogeneous binding to poly (dA-dT) · poly (dA-dT), but more than one type of intercalation site for calf thymus DNA and poly (dG-dC) · poly(dG-dC). Fluorescence spectroscopy shows that for free quinacrine the pK = 8.1 between the mono- and diprotonated states also remains unchanged in the excited state. Quinacrine bound to calf thymus DNA and polynucleotides exhibits light absorption typical for the intercalated diprotonated form. The fluorescence enhancement of quinacrine bound to poly (dA-dT) · poly(dA-dT) may be due to shielding from water interactions involving transient H-bond formation. The fluorescence quenching in poly(dG-dC) · poly(dG-dC) may be due to excited state electron transfer from guanine to quinacrine. © 1993 John Wiley & Sons, Inc.     

Optical studies of the interaction of 4′-6-diamidino-2-phenylindole with DNA and metaphase chromosomes

The optical absorption and fluorescence characteristics of 4-6-diamidino-2-phenylindole (DAPI) with DNA and chromosomes were studied. There is a decrease in extinction coefficient and shift in the absorption spectra to a higher wavelength when the dye binds to DNA. The fluorescence of DAPI is enhanced by both A-T and G-C base-pairs. The enhancement by A-T rich is significantly greater than by G-C rich DNA. The dye produces a localized bright fluorescence in centromeric regions of mouse chromosomes and the constrictions of human chromosomes 1 and 16; these regions are known to contain A-T rich DNA and show dull fluorescence when treated with quinacrine. This dye may be useful for identifying A-T rich region in chromosomes. The fluorescence of DAPI bound to polynucleotides or chromosomes is partially quenched by the introduction of BrdU. This suppression of dye fluorescence allows optical detection of sister chromatid exchanges and chromosome region containing DNA with an unequal distribution of thymidine between polynucleotide chains after BrdU incorporation.     

Mechanisms of chromosome banding. V. Quinacrine banding.

A series of biochemical investigations were undertaken to determine the mechanism of Q-banding. The results were as follows: 1. In agreement with previous studies, highly AT-rich DNA, such as poly(dA)-poly(dT), markedly enhanced quinacrine fluorescence while GC containing DNA quenched fluorescence. These effects persisted at DNA concentrations comparable to those in the metaphase chromosome. 2. Studies of quinacrine-DNA complexes in regard to the hypochromism of quanacrine, DNA Tm, DNA viscosity, and equilibrium dialysis, indicated the quinacrine was bound be intercalation with relatively little sid binding. 3. Single or double stranded nucleotide polymers, in the form of complete or partial helices, were 1000-fold more effective in quenching than solutions of single nucleotides, suggesting that base stacking is required for quenching. 4. Studies of polymers in the A conformation, such as transfer RNA and DNA-RNA hybrids, indicated that marked base tilting does not affect the ability of nuclei acids to cause quenching or enhancement of quinacrine fluorescence. 5. Salts inhibit the binding of quinacrine to DNA. 6. Spermine, polylysine and polyarginine, which bind in the small groove of DNA, inhibited quinacrine binding and quenching, while histones, which probably bind in the large groove, had little effect. This correlated with the observation that removal of histones with acid has no effect on Q-banding. 7. Mouse liver chromatin was separated into five fractions. At concentrations of quinacrine from 2 times 10-6 to 2 times 10-5 M all fractions inhibited to varying degrees the ability of the chromatin DNA to bind quinacrine and quench quinacrine fluorescence. At saturating levels of quinacrine two fractions, the 400 g pellet (rich in heterochromatin) and a dispersed euchromatin supernatant fraction, showed a decreased number of binding sites for quinacrine. These two fractions were also the richest in non-histone proteins. 8. DNA isolated from the different fractions all showed identical quenching of quinacrine fluorescenc. 9. Mouse GC-rich, mid-band, AT-rich, and satellite DNA, isolated by CsCL AND Cs-2SO-4-Ag+ centrifugation all showed identical quenching of quinacrine fluorescence, indicating that within a given organism, except for very AT or GC-rich satellites, the variation in base composition is not adequate to explain Q-banding.We interpret these results to indicate that: (a) quinacrine binds to chromatin by intercalation of the three planar rings with the large group at position 9 lying in the small groove of DNA, (b) most pale staining regions are due to a decrease binding of quinacrine, and (c) this inhibition of binding is predominately due to non-histone proteins.     

Mechanisms of chromosome banding

A series of biochemical investigations were undertaken to determine the mechanism of Q-banding. The results were as follows: 1. In agreement with previous studies, highly AT-rich DNA, such as poly(dA)-poly(dT), markedly enhanced quinacrine fluorescence while GC containing DNA quenched fluorescence. These effects persisted at DNA concentrations comparable to those in the metaphase chromosome. 2. Studies of quinacrine-DNA complexes in regard to the hypochromism of quinacrine, DNA Tm, DNA viscosity, and equilibrium dialysis, indicated the quinacrine was bound by intercalation with relatively little side binding. 3. Single or double stranded nucleotide polymers, in the form of complete or partial helices, were 1000-fold more effective in quenching than solutions of single nucleotides, suggesting that base stacking is required for quenching. 4. Studies of polymers in the A conformation, such as transfer RNA and DNA-RNA hybrids, indicated that marked base tilting does not affect the ability of nucleic acids to cause quenching or enhancement of quinacrine fluorescence. 5. Salts inhibit the binding of quinacrine to DNA. 6. Spermine, polylysine and polyarginine, which bind in the small groove of DNA, inhibited quinacrine binding and quenching, while histones, which probably bind in the large groove, had little effect. This correlated with the observation that removal of histones with acid has no effect on Q-banding. 7. Mouse liver chromatin was separated into five fractions. At concentrations of quinacrine from 2×10^?6 to 2×10^?5 M all fractions inhibited to varying degrees the ability of the chromatin DNA to bind quinacrine and quench quinacrine fluorescence. At saturating levels of quinacrine two fractions, the 400 g pellet (rich in heterochromatin) and a dispersed euchromatin supernatant fraction, showed a decreased number of binding sites for quinacrine. These two fractions were also the richest in non-histone proteins. 8. DNA isolated from the different fractions all showed identical quenching of quinacrine fluorescence. 9. Mouse GC-rich, mid-band, AT-rich, and satellite DNA, isolated by CsCl and Cs₂SO₄-Ag⁺ centrifugation all showed identical quenching of quinacrine fluorescence, indicating that within a given organism, except for very AT or GC-rich satellites, the variation in base composition is not adequate to explain Q-banding. — We interpret these results to indicate that: (a) quinacrine binds to chromatin by intercalation of the three planar rings with the large group at position 9 lying in the small groove of DNA, (b) most pale staining regions are due to a decrease binding of quinacrine, and (c) this inhibition of binding is predominately due to non-histone proteins.     

Interaction of quinacrine mustard with mononucleotides and polynucleotides

1. The interaction between quinacrine mustard and mononucleotides and polynucleotides was investigated by fluorimetry and absorbance spectrophotometry. 2. The fluorescence spectrum of quinacrine mustard is independent of the ionic strength and pH. The dependence of the quinacrine mustard fluorescence intensity on ionic strength, pH and anions is described. 3. The fluorescence intensity of quinacrine mustard was enhanced with the mononucleotide adenylic acid and polynucleotides such as poly(rA), poly(rU) and poly(rA,rU). 4. Quenching of the fluorescence intensity of quinacrine mustard occurred with the mononucleotide guanylic acid and with poly(rG) and poly(rC,rG). 5. The mononucleotide cytidylic acid or poly(rC) showed no effect on the fluorescence intensity of quinacrine mustard. 6. The interaction between the dye and native DNA species was also dependent on the presence of base-specific binding sites in the DNA. The higher the (G+C) content was in the native DNA tested the higher was the quenching effect on the fluorescence intensity of quinacrine mustard. 7. No interaction was found between the dye and methylated DNA. The binding between quinacrine mustard and apurinic DNA was confirmed to be in the phosphate groups of the purines.     

Quantitation of secretion by rat basophilic leukemia cells by measurements of quinacrine uptake

A novel method for quantitating secretion is described based on measurements of the cellular uptake of the fluorescent aminoacridine dye quinacrine into low-pH secretory granules. The quinacrine fluorescence remaining in the medium was found to decrease after incubation with increasing numbers of the 2H3 rat basophilic leukemia line. This depletion of dye from the medium decreased after a secretory stimulus. Assuming that quinacrine partitions according to mass action, a quantitative model was derived to allow calculation of the percent secretion from dye uptake data. A good correlation was obtained when the values for the percent secretion determined by the quinacrine uptake method were compared with secretion measured by release of the granule enzyme beta-glucuronidase.     

Mechanistic differences in the energy-linked fluorescence decreases of 9-aminoacridine dyes associated with bovine heart submitochondrial membranes

(1) The pH dependence of the fluorescence intensities of 9-aminoacridines associated with energized submitochondrial membranes suggests that a mechanism(s) other than protonation of the dye molecules, as is the case with quinacrine, is responsible for the energy-linked fluorescence decreases of 9-aminoacridine and 9-amino-3-chloro-7-methoxyacridine (9-ACMA). (2) That the fluorescence polarization of quinacrine associated with submitochondrial membranes more than doubles upon energization of the membranes is attributed to: (i) the bulky side chain at the 9-position of the acridine moiety which hinders the molecular rotation of quinacrine and (ii) electrostatic forces resulting from the protonation of quinacrine . H+ which induce tight binding between the dye molecules and the membranes. (3) The protonation of quinacrine associated with energized membranes, from the monoprotonated to the diprotonated species, takes place in the membrane phase, as evidence by the observation of a 'break' in both the Arrhenius plot of the respiratory rate and the plot of fluorescence polarization as a function of temperature. (4) That the measured fluorescence polarization of both 9-aminoacridine and 9-ACMA associated with both energized and nonenergized membranes is nearly zero suggests that the emitting species of these dye molecules are those in the 'free' form and that the membrane-bound molecules have formed nonfluorescent complexes; consequently no polarization can be measured.     

Quinacrine binds to the lipid-protein interface of the Torpedo acetylcholine receptor: a fluorescence study.

It has been argued both that there is a high affinity noncompetitive inhibitor binding site in the lumen of the acetylcholine receptor and that this lumen exists on the central axis of the receptor. Such a site would be expected to be 20-40 A from the membrane lipids. We tested whether, in fact, quinacrine, a potent fluorescent noncompetitive inhibitor, binds to such a site. We measured quenching of receptor-bound quinacrine fluorescence by fluorescence dipolar energy transfer to lipid probes, 5-(N-dodecanoylamino)eosin and N-(3-sulfopropyl)-4-(p-didecylaminostyryl)pyridinium, or by collision with paramagnetic lipid probes 2,2,6,6-tetramethylpiperidine-1-oxyl and 3-doxyl-17 beta-hydroxy-5 alpha-androstane (spin-labeled androstane). Initial control experiments established that in the presence of carbamylcholine, quinacrine binds to a phencyclidine-sensitive site on the Torpedo receptor with a Kd equal to 0.14 microM and with a quantum yield of 0.18. Fluorescence energy transfer from receptor-bound quinacrine had a magnitude consistent with quinacrine being less than 10 A from the lipid fluorescent probes. 2,2,6,6-Tetramethylpiperidine-1-oxyl and spin-labeled androstane were two to five times more effective at quenching receptor-bound quinacrine fluorescence than the fluorescence from membrane-partitioned 5-(dodecanoylamino)fluorescein. These results suggest that the quinacrine binding site is too close to the lipid domain to be in the lumen of the receptor, and therefore it is probably located on the outer surface of the membrane-spanning domain of the acetylcholine receptor.     

The action of ionizing radiation on DNA in the presence of quinacrine

It is shown by UV absorption and absolute fluorescence spectroscopy of solutions containing both DNA and quinacrine that the components experience mutual radio-protection due to scavenging of water radicals. From measurements at different ionic strengths it is inferred that quinacrine bound to DNA is more efficiently protected than the free compound. Furthermore, release of bound quinacrine from DNA is observed at higher doses.     

The distribution of quinacrine on chromosomes as determined by X-ray microanalysis

The distribution of quinacrine in relation to Q-banding on CHO chromosomes has been investigated using X-ray microanalysis. Technical problems involved in this type of experiment were studied in detail. It was necessary to use a solution of quinacrine acetate in acetic acid to ensure that the only chlorine detectable in quinacrine-stained chromosomes was in the quinacrine molecule. Electron irradiation during analysis rapidly destroys quinacrine fluorescence, but the chlorine is not lost from the chromosomes, and there are several reasons for supposing that a reliable distribution of quinacrine on the chromosome can be obtained by the method. — Small variations along the chromosome in the amounts of chlorine (representing quinacrine) and of phosphorus (mainly DNA) occur. The distribution patterns for chlorine and phosphorus show a good resemblance to each other for each homologous chromosome; quinacrine fluorescence patterns (Q-bands) do not resemble chlorine distribution patterns, however. The results of this study therefore support the view that Q-bands result from the differential quenching of fluorescence along chromosomes to which the quinacrine is essentially uniformly bound, and do not reflect differential binding of quinacrine along the chromosome.With an Appendix by A. D. Carothers and D. Rutovitz     

Fluorescence analysis of G·C versus A·T binding of quinacrine to DNA

The affinity of quinacrine for native DNA has been determined from fluorescence measurements and equilibrium dialysis in Tris-HC10.05 m, NaCl0.1 m, EDTA 10^?3m, pH 7.5. When considering M. lysodeiktikus, E. coli calf thymus and C. perfringens the affinities of DNA for quaniactive have been found to change by a factor of two and the fluorescence intensities to change by a factor of 25. The varying affinities and fluoroescence intensities of bound quinacrine are attributed to heterogeneous binding. For all DNAs we have assumed that there exist three classes of intercalation sites: I, A·T-A·T; 2, G·C-G·C; and 3, A·T-G·C, assuming that base pair ordering is less relevant than base composition of sites. By fitting the affinities of native DNAs with this model it was found that quinacrine binds to site 2 three times more strongly than it does to site 1. When flucrescence intensity is studied, triplets of A·T pairs appear to be responsible for the high quantum yield of A·T rich DNA whereas the quenching properties of a G·C base pair adjacent to an intercalated quinacrine are well known.     

Use of Hoechst fluorescent probe 33258 for quantitative analysis of intracellular binding of anthracycline antibiotics to DNA]

The paper deals with development of a procedure for quantitative determination of the share of anthracycline antibiotics bound in cells directly to DNA. A DNA-specific Hoechst fluorescence dye 33258 was used for the purpose. The level of its quenching on DNA correlated with the quantity of the antibiotic bound to it. It was shown that the quenching of the Hoechst fluorescence dye bound to DNA was not due to the dye competition with the antibiotic for the site of bounding on DNA, as was suggested earlier. It was likely to be defined by reabsorption of the radiation by antibiotic molecules.     

Energy-linked protonation of quinacrine in beef heart submitochondrial membranes.

1. The absorption spectrum of quinacrine in aqueous solution, in the visible region, changes with the pH of the medium in the pH range from 6.0 to 9.0 with an isosbestic point at 353 nm. This indicates that the monoprotonated (quinacrine - H+) and the diprotonated (quinacrine - 2H+) forms of quinacrine at equilibrium in this pH range have a 1 to 1 stoichiometry. 2. The monoprotonated and the dipronated forms to quinacrine exhibit similar fluorescence emission spectra, but distinctive fluorescence excitation spectra. 3. The relative fluorescence quantum yields of quinacrine in aqueous media of various pH values are estimated. The relative fluorescence quantum yield of quinacrine at pH 9.0 is more than 3 fold of that at pH 6.0. 4. The fluorescence excitation and emission spectra, as well as the relative fluorescence quantum yield of quinacrine associated with non-energized submitochondrial membranes, are similar to those of quinacrine alone. 5. Analyses of the absorption spectra, the fluorescence excitation spectra and the relative fluorescence quantum yield indicate that the energy-linked fluorescence decrease of quinacrine associated with the energized submitochondrial membranes results from the protonation of quinacrine - H+ to form quinacrine - 2H+. 6. Quantitative data are provided indicating that the maximal efficiency of protonation of quinacrine - H+ to form quinacrine - 2H+ depends on the concentration of H+ in the membranes generated through energy coupling, and the concentration of quinacrine - H+ initially present in the reaction medium. Under optimal conditions virtually complete conversion of quinacrine - H+ into quinacrine - 2H+ is observed. 7. The fluorescence intensity of quinacrine, either alone or associated with non-energized submitochondrial membranes, decreases with increasing temperature. When quinacrine is associated with the energized membranes, however, its fluorescence intensity increases slightly with increasing temperature. This unusual fluorescence behavior towards temperature, together with the fact that under optimal conditions virtually all the quinacrine molecules associated with the energized membranes are in the diprotonated form, further substantiate our earlier conclusion that the diprotonated quinacrine molecules are tightly bound to the energized membranes in a fashion which does not permit ready equilibration with the external medium.     

Molecular basis of chromosome banding

The effects of mouse satellite, main band and total DNA on the fluorescence intensity of quinacrine and of the bibenzimidazole derivative Hoechst 33258 were tested in solution. No significant differences were noticed between the double-stranded DNAs in spite of the 5% difference in AT-content between satellite and main band DNA. Single-stranded DNAs enhanced the fluorescence intensity of Hoechst 33258 far less than double-stranded DNAs. Having been denaturated and then reassociated the DNA fractions were intermediate in their enhancing effects on the fluorescence intensity of Hoechst 33258, the differences presumably being due to different degrees of reassociation. The effect of denatured and subsequently reassociated satellite DNA on the fluorescence intensity of quinacrine was similar to that of the native DNAs. Main band and total DNA quenched the fluorescence intensity of quinacrine more after denaturation-reassociation than it did when native. In the discussion the results are related to known cytological data.     

Calibration of the response of 9-amino acridine fluorescence to transmembrane pH differences in bacterial chromatophores

The spectral characteristics of absorption and fluorescence emission of 9-amino acridine are not altered by the interaction with bacterial chromatophores, except for the attenuation of both the absorption and emission following the formation of a protonic gradient. The lifetime of fluorescence of the dye is significantly affected in the presence of membranes, and even more following illumination. The shortening of the lifetime induced by light is reversible and prevented by nigericin and K+. The onset kinetics of the fluorescence quenching following the generation of an artificial transmembrane pH difference is temperature dependent, with an activation energy of 17 +/- 3 kcal/mol. The effect of pH on the rate constants is consistent with a model assuming that the diffusion of the unprotonated species is the limiting step in the quenching phenomenon. The response of 9-amino acridine to artificially imposed delta pH's has been utilized as a calibration method for the measurements of the light-induced protonic gradient. The apparent inner volume of chromatophores, evaluated from the extraplation of the response at delta pH = 0, was found to be much larger (15- to 40-fold) than the true osmotic volume, indicating that most of the dye is bound to the membrane when accumulated into the inner lumen.     

Acetylcholine receptor. Binding properties and ion permeability response after covalent attachment of the local anaesthetic quinacrine.

Membrane vesicles rich in nicotinic acetylcholine receptor prepared from Torpedo californica electric tissue have been irreversibly modified with quinacrine mustard, an alkylating derivative of the local anaesthetic quinacrine. The reaction blocked the ion channel regulated by the acetylcholine receptor. Acetylcholine still bound to the modified membrane vesicles with KD approx. 10(-8). The number of binding sites was reduced by up to 50%. Stopped-flow experiments showed that in contrast to what had been found with the reversibly binding quinacrine no fluorescence changes caused by energy transfer from the irradiated protein to the fluorescent local anaesthetic occurred after addition of agonist. This indicates that the conformational changes associated with the activation of the ion channel are blocked by the covalent reaction with quinacrine mustard. Analysis of the membrane vesicles by SDS-polyacrylamide gel electrophoresis showed that all polypeptide chains assumed to be part of the receptor complex had reacted with the mustard. Even small components, probably lipids, migrating with the dye front, showed fluorescence.     

In situ localization and characterization of different classes of chromosomal DNA: acridine orange and quinacrine mustard fluorescence

In situ denaturation of metaphase chromosomes with alkali results in a shift from green to yellow, orange, brown and red fluorescence with acridine orange, indicating increasing denaturation of chromosomal DNA. The kinetics and characteristics of denaturation are described. Mouse and Microtus agrestis chromosomes denature uniformly but human cells show sequential denaturation. With increasing concentrations of alkali, the secondary constrictions in chromosomes 1, 9 and 16 are the first, and the distal half of the Y chromosome the last, to become denatured. — Reassociation of chromosomal DNA occurs within seconds after the start of incubation in salt solution. Areas containing repetitious DNA, e.g. mouse centromeres, fluoresce much more strongly than other regions with acridine orange after prolonged reassociation. Since human and Microtus centromeric regions behave similarly, it is proposed that they, too, contain repetitious DNA. — Reassociation treatment leads to enhancement of bright quinacrine mustard fluorescence in regions already bright before treatment. Furthermore, regions containing repetitious DNA, e.g. the secondary constrictions in human chromosomes 1, 9 and 16, whose fluorescence is dull before treatment, turn bright after reassociation. — The methods of fluorescence analysis of mammalian chromosomes with acridine orange and quinacrine mustard permit the localization and study of different classes of chromosomal DNA.     

Chromosome condensation and Hoechst 33258 fluorescence in meiotic chromosomes of the grasshopper Spathosternum prasiniferum (Walker)

Patterns of Hoechst 33258 fluorescence have been studied in grasshopper chromosomes. At metaphase of mitotic as well as meiotic divisions — when chromosomes were maximally compact — all the chromosomes fluoresced brightly but no differentially fluorescing regions were detected. However, when all the chromosomes, except the X, were highly extended at pachytene and diplotene stages a distinct differential fluorescence was observed: only the centromeres of the autosomal bivalents fluoresced brightly whereas the entire X univalent showed bright fluorescence. Restriction of differentially bright fluorescence to the more condensed regions of chromosomes suggests a modulatory role for chromosome condensation in the production of Hoechst fluorescence. This suggestion was further strengthened by the substantial quenching of fluorescence caused by removal of chromosomal proteins following treatment with H₂SO₄. Similarly, post-C-band-treatment staining with Hoechst also led to quenching, though now the centromeres of the chromosomes, including the X, retained their differential fluorescence. It is proposed, therefore, that in grasshopper chromosomes, H-fluorescence is modulated by chromosome condensation brought about by differential ratios of DNA/protein at different chromosome regions and at different division stages.     

Effect of copper ions on the photochemical activity of quinacrine and its interaction with DNA

The influence of cuprum ions on the interaction between the antimalarial drug quinacrine (QA) and DNA is studied by polarized laser luminescence spectroscopy and fluorescence microscopy at molecular and cellular levels. An alteration of quinacrine luminescence intensity in complex with DNA caused by cuprum ions is explained in terms of redistribution of QA molecules from quenching GC- to fluorescent AT-DNA binding sites due to the competition of Cu2+ with the dye. Mechanisms of component interactions in the triplex "DNA-QA-Cu2+" in model and cellular systems are shown to be in qualitative agreement. QA photodynamic activity change caused by Cu2+ action is explained on the basis of the ideas being developed.