On the nature of interaction between proflavine and DNA

The role of ground state complexation in the electron transfer quenching of methylene blue fluorescence by purine nucleotides

The effect of three purine nucleotides on the fluorescence of methylene blue in aqueous buffer has been investigated. Guanosine-5'-monophosphate (GMP) and xanthosine-5'-monophosphate cause fluorescence quenching while adenosine-5'-monophosphate causes a red shift in the fluorescence maximum. All three nucleotides form ground state complexes with the nucleotides as indicated by absorption spectroscopy. The fluorescence changes at nucleotide concentrations less than 30 mM are best described by a static mechanism involving the formation of non-fluorescent binary and ternary complexes in competition with dimerization of the dye. Quenching of the fluorescence decay (tau = 368 ps) at high GMP concentrations (10-100 mM) occurs at the rate of diffusion. The mechanism of fluorescence quenching may involve electron transfer within the singlet excited dye-nucleotide complex although published values of the oxidation potentials of various purine derivatives would suggest that all three nucleotides should cause quenching. Evidence for electron transfer was obtained from flash photolysis experiments in which 100 mM GMP was found to cause the appearance of a long lived transient species absorbing in the region expected for semimethylene blue.

Inactivation and mutagenesis of herpes virus by photodynamic treatment with therapeutic dyes

Dyes which photosensitize membranes may be clinically useful for photodynamic treatment (PDT) of Herpes simplex virus (HSV) infections. It is important to determine whether the enveloped HSV can be inactivated via membrane damage without affecting the genetic material. Selection of appropriate PDT conditions, including the choice of dye, could minimize viral mutagenesis. We determined the mutagenesis caused by PDT employing three membrane-photosensitizing dyes of potential use in cancer photochemotherapy (Photofrin II, polyhematoporphyrin esters, zinc phthalocyanine tetrasulfonates) and a DNA-photosensitizing dye (proflavine sulfate). The effects were compared to those caused by exposure of HSV to ultraviolet radiation (UV). The procedure consisted of incubating HSV with microgram/ml (microM) concentrations of the dye, irradiating the samples with broad spectrum visible/near-UV radiation (Daylight fluorescent lamps) and assaying the survival of the treated HSV. Zinc phthalocyanine was the most potent dye per absorbed photon for inactivating HSV. In parallel with determination of survival, progeny of the surviving virus were grown for determination of mutagenesis. The progeny virus was harvested and subsequently assayed in the presence and absence of 40 micrograms/ml iododeoxycytidine (ICrd) to determine the frequency of mutation to ICrd resistance. Mutation frequencies were determined for progeny from the 1-4% survival level. For PDT with each membrane-photosensitizing dye, only zinc phthalocyanine increased the mutation frequency over the untreated control. This increase was less than 2-fold. Proflavine increased the mutation frequency 2-3 fold over the untreated control. Ultraviolet produced a 15-20 fold increase over the untreated control.(ABSTRACT TRUNCATED AT 250 WORDS)

A high-sensitivity differential scanning calorimetric study of the interaction of melittin with dipalmitoylphosphatidylcholine fused unilamellar vesicles

High-sensitivity differential scanning calorimetry has been used to examine the interaction of bee venom melittin with dipalmitoylphosphatidylcholine fused unilamellar vesicles. Experiments were performed under conditions for which melittin in solution is either monomeric (in low salt) or tetrameric (in high salt). It was found that under both sets of conditions melittin abolishes the pretransition at a relatively high lipid-to-protein molar incubation ratio, Ri (about 200) and that at intermediate values of Ri it broadens the main transition profile and reduces the transition enthalpy. This provides evidence which suggests that melittin is at least partially inserted into the apolar region of the bilayer. Evident at low values of Ri are two peaks in the lipid thermal transition profiles, which may arise from a heterogeneous population of lipid vesicles formed through fusion induced by melittin, or by lipid phase separation. For those profiles which exhibited only one peak, transition enthalpies, normalized to those of the lipid in the absence of the protein, are plotted vs. the bound protein-to-lipid molar ratios for the experiments performed under the conditions which give monomeric and tetrameric melittin in solution. These plots yield straight lines, the slopes of which give the number of lipid molecules each protein molecule excludes from participating in the phase transition. These were found to be 9.9 +/- 0.7 and 4.1 +/- 0.5 for monomeric and tetrameric melittin, respectively. The results are discussed in terms of possible models for the binding of melittin to phospholipid vesicles. For simple hexagonal packing of lipid molecules, incorporation as an aggregate is favored when melittin is tetrameric in solution, whereas incorporation as a monomer is favored when melittin is monomeric in solution. For low-salt solutions, evidence is obtained for the contribution of free melittin to lipid fusion, perhaps by the formation of protein bridges between apposed vesicles.

Perturbations to the intersystem crossing of proflavin upon binding to DNA and poly d(A-IU) from triplet-delayed emission spectroscopy

The steady-state prompt fluorescence, phosphorescence and delayed fluorescence spectra and triplet lifetimes of free proflavin and proflavin bound to native DNA and alternating poly d(A-IU) were obtained as a function of temperature in a buffer-glycerol solvent. The intensity of the proflavin E-type delayed fluorescence (DF) relative to both the phosphorescence (Ph) and the prompt fluorescence (F) was observed to increase with temperature, and plots of both ln (DF/Ph) and ln (DF/(F.tau T] as a function of 1/T were linear over a wide range of temperatures. Although the activation energies for the thermal repopulation of the proflavin excited singlet state from the triplet obtained from the slopes of these plots were essentially unchanged on binding, perturbations to the S1----T1 intersystem crossing rate constants extracted from the intercepts at infinite temperature were observed. The marked enhancement of the intersystem crossing that occurs with binding to the iodinated polynucleotide reflects an external heavy atom perturbation upon the intercalated dye which also induces a shortening in the triplet lifetime. With proflavin bound to DNA an enhancement to the S1----T1 intersystem crossing, though lesser in magnitude than for poly d(A-IU), is observed but with no change to the triplet lifetime. The well-studied fluorescence quenching of DNA-bound proflavin is a result of this increase in the intersystem crossing. It is proposed that these non-heavy atom enhancements in the intersystem crossing are due to distortions of the molecular plane of the bound proflavin molecule. In total these analyses provide a complete description of the excited state processes of the proflavin molecule and their variations with temperature.

Effects of bee venom melittin on the order and dynamics of dimyristoylphosphatidylcholine unilamellar and multilamellar vesicles

The effects of bee venom melittin on the order and dynamics of dimyristoylphosphatidylcholine unilamellar and multilamellar vesicles at a protein-to-lipid molar ratio of 1:60 have been investigated by employing the techniques of nanosecond emission anisotropy with 1,6-diphenyl-1,3,5-hexatriene as the fluorescent probe, enhancement by polar groups of the weakly allowed 0-0 vibronic transition in the fluorescence spectrum of pyrene, and Raman spectroscopy. The emission anisotropy results, which are found to be consistent with the wobble-in-cone model, show that the protein induces an increase in the order parameter, S, of the acyl chains of unilamellar vesicles below, at, and above their phase transition temperature, Tt, and it decreases strongly the diffusion rate, Dw, only below Tt. On the other hand, for multilamellar vesicles, the protein induces a decrease in S only at Tt and does not affect Dw. These effects are consistent with the observed changes in the degree of enhancement of the 0-0 vibronic transition of pyrene. Moreover, the protein broadens the thermal transition profile of multilamellar vesicles but sharpens dramatically that of unilamellar vesicles and fuses them without changing significantly the Tt in either case. On the other hand, the Raman data detect a decrease in the inter- and intramolecular order of the acyl chains of multilamellar vesicles below Tt and a decrease of only the former Tt. This disparity between the Raman and the nanosecond emission anisotropy data is discussed in terms of differences in the time scales of the two techniques and in the state of aggregation of the lipid-bound melittin. The data for the enhancement of the 0-0 vibronic transition of pyrene suggest that, for a melittin-to-lipid ratio of 1:60, the size or structure of channels formed in the bilayer by melittin does not allow the penetration of a neutral molecule the size of pyrene deeply into the bilayer.

The binding of 9-aminoacridine to calf thymus DNA in aqueous solution. Electronic spectral studies

Absorption, circular dichroism and steady-state fluorescence spectra were determined of 9-aminoacridine solutions in the presence of DNA at an ionic strength of 0.001 mol dm-3. Up to a dye/DNA phosphorus ratio of about 0.2 the results are fully consistent with the requirements and predictions of a binding model already shown to apply to the binding of other aminoacridines to DNA. The apparently anomalous spectroscopic behaviour of the 9-aminoacridine/DNA system compared with proflavine/DNA, for example, can be satisfactorily explained from a consideration of the magnitudes of exciton interactions between dyes bound to DNA.

Biological effects of dyes on bacteria. VI. Mutation induction by acridine orange and methylene blue in the dark with special reference to Escherichia coli WP6 (polA1)

Acridine orange (AO) and methylene blue (MB) in the dark were shown to be weak to moderate mutagens (induction of resistance to T5 phage) in repair-deficient strains of Escherichia coli B/r. However, strain WP2 (wild-type) was not mutated by AO in the dark, in confirmation of earlier data. The presence of 2 microM AO reduced by 41% the spontaneous mutation rate in strain WP2, from 4.1 to 2.4 mutants/10(8) cells/generation. In the polymerase I-deficient strain WP6 (polA1), 2 microM AO increased the mutation rate in the dark 14-fold. We propose that both spontaneous and AO-induced mutagenesis in the absence of light occur at the site of semiconservative DNA replication. If the intercalation mechanism for the effects in the absence of light is valid, the wild-type strain (WP2) may be resistant to frameshift mutagenesis induced by intercalated compounds, while the polymerase I-deficient strain (WP6) may be highly suceptible to the presence of an intercalated dye such as AO at the DNA-replication fork. MB and AO likely act through different mechanisms since MB is only a moderate mutagen in strain WP6 and the other repair-deficient strains tested.

Fluorescence decay studies of the DNA-3,6-diaminoacridine complexes

The interaction of several 3,6-diaminoacridines with DNAs of various base composition has been studied by steady-state and transient fluorescence measurements. The acridine dyes employed are of the following two classes: class I - proflavine, acriflavine and 10-benzyl proflavine; class II - acridine yellow, 10-methyl acridine yellow and benzoflavine. It is found that the fluorescence decay kinetics follows a single-exponential decay law for free dye and the poly[d(A-T)]-dye complex, while that of the dye bound to DNA obeys a two-exponential decay law. The long lifetime (tau 1) for each complex is almost the same as the lifetime for the poly[d(A-T)]-dye complex, and the amplitude alpha 1 decreases with increasing GC content of DNA. The fluorescence quantum yields (phi F) of dye upon binding to DNA decrease with increasing GC content; the phi F values for class I are nearly zero when bound to poly(dG) X poly(dC), but those for class II are not zero. This is in harmony with the finding that GMP almost completely quenches the fluorescence for class I, whereas a weak fluorescence arises from the GMP-dye complex for class II. The fluorescence spectra of the DNA-dye complexes gradually shift toward longer wavelengths with increasing GC content. In this connection, the fluorescence decay parameters show a dependence on the emission wavelength; alpha 1 decreases with an increase in the emission wavelength. In view of these results, it is proposed that the decay behavior of the DNA-dye complexes has its origin in the heterogeneity of the emitting sites; the long lifetime tau 1 results from the dye bound to AT-AT sites, while the short lifetime tau 2 is attributable to the dye bound in the vicinity of GC pairs. Since GC pairs almost completely quench the fluorescence for class I, partly intercalated or externally bound dye molecules may play an important role in the component tau 2.

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.

Melittin-phospholipid interaction studied by employing the single tryptophan residue as an intrinsic fluorescent probe

The rotational correlation time of melittin, obtained from the nanosecond anisotropy of the emission from its single tryptophan residue, has been found to increase considerably in phosphate solution relative to that in aqueous solution, consistent with protein aggregation. The steady-state fluorescence spectra as well as the absorption spectra in phosphate solution exhibit a very good degree of similarity with those of the protein bound to egg phosphatidylcholine (PC) and distearoylphosphatidylcholine (DSPC) bilayer liposomes. The value of the second-order rate constant for dynamic quenching, kq = 1.4.10(9) M-1.s-1, by acrylamide in 0.5 M phosphate solution is comparable to those for the protein-phospholipids complexes (1.10(9) and 0.7.10(9) M-1.s-1 for egg PC and DSPC, respectively). Similarities are also found in the nanosecond properties. There is a much stronger and quite similar dependence of the fluorescence spectra on time in the nanosecond range and of the fluorescence decay times on the emission wavelength in both cases as compared to the case is aqueous solution. These observations support the notion that melittin binds to the phospholipids in an aggregated form. The results suggest that the reduction in the kq values of bound melittin relative to that in aqueous solution and the blue shift of the fluorescence spectrum (from 352 to 337 nm) are brought about by shielding of the tryptophan residue from the solvent through a combination of protein aggregation and enhancement of its alpha-helical content (suggested by published CD data). The magnitude of the kq values for bound melittin, however, is still relatively high implying the occurrence of rather frequent encounters between the tryptophan residue and the hydrophilic acrylamide molecules. Thus, the residue is found not to penetrate deep into the phospholipid bilayer.

Phase transitions and cholesterol effects in phospholipid liposomes. A new method employing the enhancement of the O-O vibronic transition of pyrene

The enhancement of the weakly allowed 0-0 vibronic transition in the fluorescence spectrum of the probe pyrene, which we previously showed to result from ground-state complexation with polar groups, has been shown in the present study to offer a new method for determining phase transition temperatures of liposomes and for studying the effects of cholesterol on the structure of their semipolar glycerol backbone. For dipalmitoylphosphatidylcholine it is found that small cholesterol contents (approximately 9 mol%) induce an increase in the polarity of the microenvironment of the probe, whereas contents greater than or equal to 13 mol% induce a decrease in the polarity. The results are discussed in terms of cholesterol effects on the frequency and extent of thermally-induced structural fluctuations which, in turn, affect the penetration of the probe into the bilayer.

Dependence of the mutagenic power of heteroatomic dyes on their DNA-base-pair specificity

23 compounds structurally related to proflavine were tested with Salmonella typhimurium TA1537 for their ability to induce mutants in the quantitative mutagenicity test of Ames et al. Of these compounds, 13 were mutagenic. Their mutagenic power decreased with increasing GC specificity of the dye. Because the mutational site in the tester strain is assumed to consist of a run of 4 adjacent GC pairs of the same polarity we conclude that for mutation to occur the dye should not be bound within this run of identical base pairs. Some of the compounds showed a negative slope at higher concentrations. Because these dyes also showed a comparatively high tendency to dimerize we conclude that mutation induction requires the intercalator to be bound as a monomer. Those compounds that were not mutagenic either did not intercalate or were inactivated by reduction.

Photodynamic effects of dyes on bacteria. III. Mutagenesis by acridine orange and 500-nm monochromatic light in strains of Escherichia coli that differ in repair capability

In the presence of acridine orange (AO) and monochromatic 500-nm light, the recombination-deficient strain of Escherichia coli, WP10 (recA), showed a 15-fold increase in mutation rate over the wild-type (WP2) strain. Under the same conditions, strain Bs--1 (uvrB lexA lon) showed a 5-fold increase in mutation rate over strain WP2. In contrast, the endonuclease-deficient, strain, WP2s (uvrA), showed a lower AO-500 nm mutation rate than wild-type. The extremely high mutation rate of the recA strain cannot be due to error-prone inducible SOS repair since the inducible recA + function is absent. Repair of the AO-500 nm-induced lesions is likely due to a recA+-dependent, error-free, recombination process. It is concluded that the high mutation rates with AO-500 nm light obtained in chemostat cultures of recA and lexA strains occur as a consequence of errors during semi-conservative DNA replication in the presence of unrepaired DNA lesions.

Interaction of phenosafranine with nucleic acids and model polyphosphates. III. Heterogeneity in phenosafranine interactions with DNA base pairs

Fluorescence and circular dichroism spectral measurements, thermal denaturation studies and binding competition experiments with netropsin and actinomycin D were carried out in systems containing phenosafranine bound to DNA's differing in base composition. The investigated properties exhibit a heterogeneity related to the content of A.T and G.C pairs in DNA and to the nature of phenosafranine binding modes. At low level of saturation of binding sites (r less than 0.1) phenosafranine does not show strong preference for any of the DNA base pairs in the overall binding. However, the strong monomer non-cooperative binding outside the helix (mode I1) occurs predominantly, even though not exclusively in G.C rich regions. The strong binding modes involving intercalated dye molecules (mode I2 and eventually mode II1) prevail in A.T rich regions. These binding modes become the principal types of strong phenosafranine interaction with DNA when the level of saturation of binding sites increases, i.e. at r greater than 0.1.20

Fluorescence decay and quantum yield characteristics of acridine orange and proflavine bound to DNA

Fluorescence properties (quantum yield, decay curve, lifetime and polarization) of acridine orange and proflavine bound to DNA were examined as a function of nucleotide to dye (P/D) ratio. First, mean fluorescence lifetimes were determined by the phase-shift measurements. The lifetime and quantum yield of acridine orange increased in a parallel fashion with increasing P/D ratio. There was no parallel relation between the lifetime and quantum yield for proflavine; the lifetime showed a minimum around P/D equals 10...