Studies on the fluorescence and binding of 8-anilino-1-naphthalene sulfonate by submitochondrial particles

Polybrominated diphenyl ether congener (BDE-100) induces mitochondrial impairment

Brominated flame retardants are used in various consumer products to increase their resistance to fire and/or high temperatures. Polybrominated diphenyl ethers (PBDEs) are representatives of this class and among the most widely used congeners, and BDE-100 is produced on a large scale. There is a lack of toxicological data about these compounds, which has recently become a matter of concern to the scientific community. The mitochondria are recognized as the main energy-producing organelles, as well as playing a vital role in the maintenance of many cell functions. Therefore, mitochondria were used in the present work as an experimental model to evaluate the effects of the BDE-100 congeners at concentrations ranging from 0.1 μM to 50 μM. The results showed that high concentrations of BDE-100 were able to induce mitochondrial alterations. It was observed that the substance had an affinity for the hydrophilic portion of the mitochondrial membrane, as monitored by ANS, inhibiting the glutamate + malate-stimulated mitochondrial respiration and also inducing dissipation of the mitochondrial membrane potential, deregulation of calcium homoeostasis and mitochondrial swelling, the latter being insensitive to cyclosporin A (CsA) but partially inhibited by Ruthenium Red and N-ethyl maleimide. In addition, a significant reduction in mitochondrial ATP content was found, but on the other hand, no oxidative stress was observed after exposure of the mitochondria to BDE-100. These results show the key role of mitochondria in the cytotoxicity induced by BDE-100.

Light scatter and DNA accessibility to propidium iodide of ataxia telangiectasia and fanconi anemia cells

Cells from individuals with genetic diseases ataxia telangiectasia (AT) and Fanconi anemia (FA) exhibit hypersensitivity to ionizing radiation (AT) or DNA cross-linking agents (FA) which may be caused by multiple factors including defects in chromatin structure and DNA repair. In this study, a combination of cytometric techniques was employed to study the chromatin conformation of AT and FA cells. Nuclei of peripheral blood mononuclear cells (PBMCs) and of skin fibroblasts established from AT and FA patients were analyzed by light scattering and fluorimetric titration with the DNA-intercalating dye propidium iodide. The light scatter measurements revealed the presence of small-sized nuclei with reduced granularity in PBMCs and fibroblasts from both AT and FA patients. The fluorometric titration data could be interpreted by assuming two classes of propidium iodide binding sites with different affinities. The number of high-affinity sites in AT and FA fibroblasts was significantly larger (by 20%) than in control cells. Our findings show the applicability of cytometric techniques for the rapid assessment of chromatin conformation and also suggest the possibility to identify AT and FA carriers.

Preferential interactions of fluorescent probe Prodan with cholesterol

The fluorescent probe Prodan has been widely used as a probe of model and biological membranes. Its fluorescent maxima in phospholipid bilayers vary as a function of phase state, with maxima at 485 for the liquid crystal Lalpha, 435 nm for the gel L'beta, and 507 nm for the interdigitated gel LbetaI phase, with excitation at 359 nm. These spectral changes have been used for the detection of phase changes among these phases. In the present study, the fluorescent properties and partition coefficients of Prodan in model membranes of phosphatidylcholines and phosphatidylethanols have been studied as a function of lipid phase state and cholesterol content. It is shown that the Prodan spectrum in the presence of cholesterol no longer reflects the known phase state of the lipid; in each phase state, the presence of cholesterol leads to a spectrum with the maximum at 435 nm, characteristic of the noninterdigitated gel phase. The partition coefficient of Prodan into these lipids also varies with the phase state, giving values of 0.35 x 10(4) in the interdigitated gel, 1.8 x 10(4) in the noninterdigitated gel, and 7. 6 x 10(4) in the liquid crystal phase. In the presence of cholesterol these partition coefficients are increased to 13 x 10(4) for the liquid crystal and the gel phase, and 5.1 x 10(4) in the presence of 100 mg/ml ethanol. These results suggest that Prodan has preferential interactions with cholesterol, and is thus not a randomly distributed fluorescent reporter probe in membranes containing cholesterol. These results suggest that Prodan should be used only with great caution in complex lipid mixtures, particularly biological membranes.

Spectrofluorometric and microcalorimetric study of the thermal poration relevant to the mechanism of thermohaemolysis

This study sheds light on the structural changes in erythrocyte membrane during thermally induced poration, an event involved in thermohaemolysis. Two major membrane disturbing events can be induced during transient heating, the denaturation of spectrin and thermoporation. The first one precedes the latter but is not involved in it. Ethanol linearly reduces the onset temperature of both events but with different efficiencies. Thermoporation efficiency exceeds by 3.5 fold that of spectrin denaturation. Thus, at a specific concentration of ethanol (18% v/v), the poration occurs at 39.5 degrees C, which precedes the denaturation of spectrin by 6 degrees C. To induce and study the poration avoiding spectrin denaturation, cells were put in contact with preheated (39 degrees C) isotonic (60mM) NaCl) media containing 18% v/v ethanol and sucrose as an osmotic protectant. After 3 min heating, the porated cells were washed, their membranes isolated and studied. The control cells were processed similarly except that they were incubated at 23 degrees C, thus avoiding thermoporation. Using scanning microcalorimetry, the enthalpy and the temperature of denaturation of spectrin were found to be the same in control as well as in porated membranes which indicates similar spectrin structure in both membranes. While the enthalpy of denaturation of the anion channel was preserved, its denaturation temperature was lowered by 2.5 degrees C after poration. These results confirmed that the heat denaturation of the main membrane proteins was not needed and not involved in thermoporation and, hence, in thermohaemolysis. Analysis of the fluorescence of membrane bound ANS gave an apparent increase in the number of binding sites for ANS in membranes after poration. In relation to the control, the eximerization of pyrene in porated membranes changed, depending on the location of the probe: in the domain of free lipids it decreased by 18% but it increased by 60% in the lipid milieu proximal to membrane proteins. Likewise, the eximerization of N-(3-Pyrene) maleimide bound to membrane proteins increased by 67% after poration, which proves increased intramolecular mobility of proteins following poration. The maximal efficiency for transferring energy from tryptophans to neighbouring pyrene was determined to be 0.93 in control, which is almost the same as in intact membranes, and 0.70 in porated membranes, indicating a strong decrease in the lipid/protein contact zone. This data suggests a mild conformational change, possibly an irreversible perturbance of the transbilayer distribution of membrane proteins in porated membranes in comparison to the control and intact ones.

Electropermeabilization and fluorescent tracer exchange: the role of whole-cell capacitance

Transmembrane crossing of charged fluorescent tracers such as propidium iodide (PI) and carboxyfluorescein+ (CF) can be used to quantitate membrane permeabilization. Murine myeloma Sp2/0-Ag14 cells were loaded with CF (0.1 fmol/cell) before electropulsation (0.5-3.0 kV/cm, 40 microseconds) in medium containing 25-50 micrograms/ml PI at 21-23 degrees C. Cytograms of PI vs. CF fluorescence showed three readily distinguishable subpopulations: 1) intact living cells with CF but without PI (these form > 95% of the prepulsed population), 2) transiently electropermeabilized but resealed cells showing both CF and low-level PI fluorescence, and 3) permanently permeabilized cells without CF but with very high PI fluorescence. Despite the ready influx of PI, the efflux of CF from transiently permeabilized cells was negligible and was insensitive to pulse parameters; however, electrically killed cells (subpopulation 3) lost all CF fluorescence and probably lost their cytoplasm. This difference in transmembrane passage of the dyes is best explained by binding of intracellular CF to macromolecules (and/or organelles). In isotonic "pulse medium," the membranes resealed after electropulsing with a time constant (tau R) of about 2 min. In 150 mOsm medium, resealing was faster (typically tau R approximately 0.5 min). The population distribution of PI uptake [coefficient of variation (CV) > 40%] was very broad and could not be accounted for by the radius dependence of pulse-induced voltage (CVradius approximately 10%). The variability in PI uptake could be explained if the electrical energy of the charged membrane, which depends on the whole-cell capacitance (Cc), was taken into account. Evaluation of the Cc values with single-cell resolution was based on measurement of the electrical charging time constant of the plasma membrane by electrorotation.

Membrane permeability transition promoted by phosphate enhances 1-anilino-8-naphthalene sulfonate fluorescence in calcium-loaded liver mitochondria

Phosphate and a number of other compounds induce membrane permeability transition (MBT) in Ca(2+)-loaded mitochondria. 1-Anilino-8-naphthalene sulfonate (ANS) was used as a fluorescent probe to investigate perturbations on the inner membrane during MBT. Induction of MBT caused ANS fluorescence enhancement with a biphasic rate that reached a plateau. The enhancement is analogous to that reported for de-energization of mitochondria. The fluorescence level was independent of whether ANS was added before or at different times after phosphate. In the absence of ANS, fluorescence was low and remained unchanged. The initial time course of MBT, as followed by large-amplitude swelling, was similar to that of fluorescence enhancement. Ruthenium red, EGTA, ADP, and cyclosporin A inhibited the enhancement. Only EGTA + ADP (or ATP) reversed the enhancement when added after phosphate. Efflux of matrix Ca2+ by sodium acetate or A23187 did not alter ANS fluorescence. The binding parameters (Kd and number of binding sites) were not significantly different, but the fluorescence maximum was more than doubled after MBT. Although the fluorescence of bound ANS showed a nonlinear relationship, it was always higher (73.0 +/- 19.0%) after reaching the plateau. Since ANS binding to membranes is nonspecific, the exact mechanism of the enhanced fluorescence is not apparent. The dependence of the initial rate of fluorescence enhancement on Ca2+ concentration was nonlinear, with 45 microM at half-maximal rate. The dependence on phosphate was hyperbolic with 0.7 mM at half-maximal rate, which is close to the Km value of phosphate carrier. The kinetics is compatible with Ca2+ binding to some membrane component(s) during MBT and cause ANS fluorescence enhancement.(ABSTRACT TRUNCATED AT 250 WORDS)

A pitfall in the use of double-reciprocal plots to estimate the intrinsic molar fluorescence of ligands bound to albumin

Double-reciprocal plots of fluorescence intensity versus protein concentration are often used to obtain the intrinsic molar fluorescence (Fb) of ligands bound to acceptor molecules such as albumin. In this paper we show that these plots develop upward concave curvature as the concentration of albumin increases. Thus linear extrapolation of such plots cannot be employed to provide accurate values of Fb. It is suggested that a direct plot of fluorescence intensity versus log protein concentration should be employed to obtain Fb.

Isoparametric analysis of binding and partitioning processes

An isoparametric method is described for the analysis of titration data pertaining to the binding of a ligand to an acceptor, or to the partition of a molecule between lipid and aqueous compartments. Where spectroscopic titrations are employed, the analysis does not require a priori choice of an association model, nor assumptions concerning a linear relationship between the spectroscopic signal and the amount of bound or partitioned ligand. The method has wide applicability and is illustrated with reference to (a) ligand-acceptor associations monitored by perturbation of the absorption or fluorescence signal of ligand or acceptor, and (b) cross-linking interactions such as those encountered in antigen-antibody precipitin reactions.

Hepatic microsomal glucose-6-phosphatase of normal and alloxan-diabetic rats. Thermotropic effects on kinetics and interaction with deoxycholate and 1-anilino-8-naphthalene sulfonate

Thermotropic effects on the kinetics of glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase, EC 3.1.3.9) activity of hepatic microsomes from normal and alloxan-diabetic rat liver were investigated by determining V, Km and Ki (substrate inhibition) values. Influence of deoxycholate (0.1%) and 1-anilino-8-naphthalene sulfonate (2.5 mM) on the kinetics was also evaluated. 1. Substrate inhibition occurred at 0.06 M for the enzyme from normal rats and at 0.0-0.025 M for the enzyme from diabetic rats. 2. The enzyme from diabetic rats showed a transition that extended between 22.7 and 27 degrees C in the Arrhenius plot (log V vs. T-1) instead of at 19.5 degrees C. 3. Deoxycholate increased the V value of both enzymes without affecting substrate inhibition at all the temperatures but did not completely abolish the transition in the Arrhenius plot of the enzyme from diabetic rats. 4. 1-Anilino-8-naphthalene sulfonate eliminated substrate inhibition and activated the enzyme of normal rats above 27.5 degrees C by increasing both V and Km values. Below this temperature, the enzyme showed biphasic or allosteric kinetics. At low substrate concentrations it was activated as both V and Km values were increased. The enzyme from diabetic rats, on the other hand, was activated at all the temperatures and exhibited linear kinetics. 5. Binding of 1-anilino-8-naphthalene sulfonate to the microsomal fraction increased with decreasing temperature as revealed by the increase of relative fluorescence. The microsomal fraction of diabetic rats showed a more anomalous fluorescence response between 13-18 degrees C. 6. Enthalpy changes for glucose 6-phosphate binding to the inhibition site were slightly larger than binding to the active site. Calculated entropies of activation for transition state complex of glucose-6-phosphatase reaction were fairly large and negative. The free energy of activation (28-30 kcal/mol) was independent of temperature and experimental conditions. 7. In the microsomal fraction (total as well as rough), phospholipid content and fatty acid unsaturation index of phospholipids were decreased after diabetes. The level of free cholesterol remained unchanged but the molar ratio of cholesterol to phospholipid increased. The different thermal response and 1-anilino-8-naphthalene sulfonate interaction to the enzyme from diabetic rat and liver could be ascribed to the altered lipid environment of the enzyme on the endoplasmic reticulum membrane.

The binding of 8-anilinonaphthalene-1-sulphonate to a fixed concentration of unenergised and succinate-energised submitochondrial particles

The effect of the approximately hyperbolic relationship between fluorochrome concentration and light absorbed on the interpretation of data for the binding of 8-anilinonaphthalene-1-sulphonate to unenergised and succinate-energised submitochondrial particles has been investigated. If this is taken into account plots of fluorescence against fluorescence x [fluorochrome]-1 do not tend towards a maximum fluorescence value. The significance of this findings is discussed.

The binding of 1-anilino-8-naphthalene sulfonate to the hemocyanin of Octopus vulgaris

The binding of 1-anilino-8-naphthalene sulfonate (ansyl) to native and copper-free hemocyanin of Octopus vulgaris has been studied in different conditions by measuring the fluorescence properties of the probe in the presence of hemocyanin. Native hemocyanin, either in the oxygenated or in the deoxygenated state, does not bind ansyl. The binding of ansyl with apohemocyanin induces a strong increase (from 0.004 to 0.6 -- 0.7) of the quantum yield and a blue shift from 520 nm to 460 nm of the emission maximum indicating the presence of ansyl binding sites in the protein. Experimental evidence is reported that the binding occurs at the copper-binding site of the protein. The dissociation constants of the ansyl-hemocyanin complexes are equal to about 10(-4) M, i.e. they are of the same order of those obtained with other proteins. The number of binding sites (n) of apohemocyanin for ansyl depends on the conformational state of the protein and ranges from 0.15 -- 0.80 mol/mol protein (Mr 50,000), depending on pH, ionic strength, and urea concentration. A negative interaction between the ansyl binding sites has been suggested.

An analysis of the binding of fluorescence probes in mitochondrial systems

Measurements of the binding of the fluorescent probes 8-anilinonaphthalene-1-sulfonate (ANS) and ethidium ions to whole and disruped mitochondria and submitochondrial particles suggest that the inner mitochondrial membrane is freely permeable to the two probes. Equations relating the binding of permeant probes to the electro-chemical balance across the membrane of vesicular systems are derived and these equations used to analyze Scatchard plots of the binding of the two probes to energized and nonenergized mitochondria and EDTA particles.

The application of fluorescent probes in membrane studies

Fluorescence has been used in biochemical studies for many years but only recently has the information content and the practical applicability of the fluorescence method been fully realized.

Following the early studies of Newton (1954) and Weber (11954) and after the initial utilization of fluorescent probes by Chance and coworkers (Azziet al.1969) and Tasakiet al.(1968), in the study of membranes, the use of fluorescence to provide structural information at microscopic or molecular levels in biological membranes has become widespread. widespread. The application of the fluorescence technique to biological systems has progressed parallel to the development of a theoretical basis for fluorescence data interpretation and the synthesis of a large number of fluorescent probes, organic molecules having fluorescence characteristics that are dependent on their environment.

8-Anilinonaphthalene-1-sulphonate interaction with whole and disrupted mitochondria: a re-evaluation of the use of double-reciprocal plots in the derivation of binding parameters for fluorescent probes binding to mitochondrial membranes

It is shown that 8-anilinonaphthalene-1-sulphonate is a permeant anion of whole mitochondrial membranes. It is also shown experimentally and algebraically that plots of reciprocal fluorescence against reciprocal membrane concentration, at a fixed 8-anilino-naphthalene-1-sulphonate concentration, are straight lines even when more than one binding site is involved.

Change of mitochondrial buffering capacity induced by propranolol

Propranolol is able to increase the amount of the titratable groups of mitochondrial membranes. This effect occurs with sonicated particles and with liposomes, too. The phenomenon is only seen in the presence of salt solutions, not in sucrose. Propranolol increases the fluorescence of anilino-naphthalene sulphonate (ANS) in mitochondrial suspensions. The increase is counteracted by increasing concentrations of potassium chloride. It is suggested that the increase of the titratable groups results from a decrease of the aggregation of the phospholipids of the membranes. At the same time the environment of the bound ANS molecules is more hydrophobic in sucrose than in potassium chloride. The amount of the buffering groups and the hydrophilicity are in direct and the amount of the buffering groups and the fluorescence of ANS in inverse correlation.