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

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.

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.

A fluorescence study of the binding of cytochrome C to mixed-phospholipid microvesicles : evidence for a preferred orientation of the bound protein

Kinetic and equilibrium experiments are reported on the binding of the fluorescent probe 1,8-anilino-naphtalene sulfonate (ANS) to microvesicles of natural lecithin containing 10 per cent of an anionic phospholipip (90 : 10 mixtures). Kinetics discriminated between fast binding to the outer leaflet of the bilayer and apparently slow binding to the inner leaflet controlled by the diffusion of the probe across the bilayer. The equilibrium distribution of ANS between the two leaflets was not dependent on the nature of the anionic species and the spectral properties of bound ANS were identical in all cases investigated. A hyperbolic saturation was observed allowing to propose an affinity scale for the binding of ANS to mixtures of lecithin with phosphatidic acid, phosphatidylinositol, and cardiolipin. The effects on binding of ionic strength and sodium dodecylsulfate were also considered. The binding of horse heart ferricytochrome c to ANS-labelled microvesicles was studied quantitatively making use of the quenching of the probes fluorescence by the heme. Perrin-Förster energy transfer could be analysed on the basis of a simple model of the physical arrangement of the system which was elaborated from published data referring to ANS and cytochrome c binding to phospholipids. Experimental and theoretical computed values of the quenching efficiency were compared and led to conclude in favor of a preferred orientation of the heme crevice fully accessible from the external space at the lipid interface.

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.

Membrane lipids as intracellular binders of chlorpromazine and related drugs

Equilibrium dialysis studies with chlorpromazine (CPZ) showed affinity and binding capacity values which were not significantly different with the following binders: rat liver microsomes, mitochondria, mitochondrial membranes, brain synaptosomes, myelin vesicles, and red blood cell membranes. There was no binding to cytosol or mitochondrial matrix. The same binding values as above were obtained with protein-free liposomes of lipids extracted from microsomes, mitochondrial and red cell membranes and of pure egg lecithin. The binding values of the two classes of binding sites of all these preparations were K1=2.7+/-1.0-10(4) M-1, K2=3.8+/-1.7-10(3) M-1, C1=580+/-+/-230 and C1+2=1410+/-500 nmole/mg phospholipid. These values were not altered by elimination of the polar head groups of phospholipids with phospholipase C. The results were confirmed by a UV spectroscopic method whereby the strongest binding signals were obtained with CPZ in the presence of fatty acids such as oleate. It is concluded that the major intracellular binders of CPZ and related drugs are the nonpolar moieties of membrane phospholipids, whereby hydrophobic interactions are mainly involved.

The adenosine triphosphatase-inhibitor content of bovine heart submitochondrial particles. Influence of the inhibitor on adenosine triphosphate-dependent reactions

1. The activity of the ATPase (adenosine triphosphatase) of phosphorylating particles prepared by sonication of bovine heart mitochondria in the presence of MgCl2 and ATP is influenced by the isolation method for the mitochondria used in the preparation of particles. Type-I particles, made from mitochondria isolated in a medium lacking succinate, have a lower ATPase activity than to Type-II particles, which are prepared from mitochondria isolated in a medium containing succinate. 2. Centrifugation under appropriate energized conditions increases the ATPase activity of Type-I particles almost to that of the Type-II particles. The ATPase activity of Type-II particles was only slightly stimulated by this procedure. These data are interpreted as indicating a higher content of the ATPase-inhibitor protein in the Type-I particles. 3. A comparison was made of the ATP-driven enhancement of 8-anilinonaphthalene-1-sulphonate fluorescence and the exchange of the endogenous tightly bound nucleotides of the ATPase in Type-I and Type-II particles. The effect of exogenous inhibitor protein on both these reactions was also studied. 4. The time-scale on which the inhibitor protein can exchange between ATPase molecules is discussed.

A kinetic analysis of the changes in fluorescence on the interaction of 8-anilinonaphthalene-1-sulphonate with submitochondrial particles

A comparison of the fluorescence change on the addition of 8-anilinonaphthalene-1-sulphonate to succinate-energized submitochondrial particles with that on the addition of succinate to submitochondrial particles incubated with 8-anilinonaphthalene-1-sulphonate shows that these changes in fluorescence may be explained solely in terms of 8-anilinonaphthalene-1-sulphonate binding. This comparison does not support the proposal of an 8-anilinonaphthalene-1-sulphonate-monitored change in the conformation of submitochondrial-particle membranes [Brocklehurst, Freedman, Hancock & Radda (1970) Biochem. J.116, 721-731]. The biphasic nature of the decrease in fluorescence, which was found to follow the addition of uncoupler to submitochondrial particles incubated with ATP or succinate, or of antimycin A to submitochondrial particles incubated with succinate, does not support the existence of 'aplectic' and 'symplectic' states of the mitochondrial membrane [Barrett-Bee & Radda (1972) Biochim, Biophys. Acta 267, 211-215].

On the nature of the energised state of submitochondrial particles; investigations with N-aryl naphthalene sulphonate probes

1. A further investigation has been made of the way in which the fluorescent probes 1-anilino-naphthalene-8-sulphonate and 2-(N-methyl-anilino) naphthalene-6-sulphonate report on the energised state of bovine heart submitochondrial particles. 2. A comparison of the probe responses to energisation with ATP or to a potassium diffusion potential has been made. The fluorescence enhancements seen in these two cases have different characteristics, and in view of this it is questioned whether a substrate generated energised state of a submitochondrial particle can be equated with a trans-membrane potassium diffusion potential. 3. Substitution of ITP for ATP reduces the rate at which either of the probes respond to energisation. In contrast reducing the ATPase activity of the particles by treatment with the covalent ATPase inhibitors 4-chloro-7-nitrobenzofurazan or N,N'-dicyclohexyl-carbodiimide has no effect on this rate. This finding that the rate of the fluorescence changes is directly sensitive to events at the level of the ATPase, but not to the total ATPase activity, suggests that this rate may not be controlled by a delocalised energised state. Reduction of ATPase activity decreases the extent of the fluorescence enhancement and a relationship between the change in probe fluorescence and ATPase activity is given. 4. The results in this paper are discussed in the context of the mechanisms which have been proposed to account for the fluorescence enhancements of N-aryl naphthalene sulphonate probes upon energisation of submitochondrial particles.

Transmembrane electrophoresis of 8-anilino-1-naphthalenesulfonate through egg lecithin liposome membranes

Valinomycin has been shown to increase the amount of 8-anilino-1-naphthalenesulfonate (ANS) bound to egg lecithin liposomes and also to increase the maximum fluorescence value, as derived from double reciprocal plots. The assay conditions were such that addition of valinomycin would not produce a transmembrane potential. The formation of a valinomycin potassium ANS complex in the micelle membrane is proposed. This could account for the increase in the maximum fluorescence value and, by acting as an ANS transporter, could also account for the increase in ANS bound. Tributylamine was also shown to increase the binding and maximum fluorescence of ANS. In assay conditions where the addition of valinomycin would produce a transmembrane potential negative inside, the tributylamine-induced fluorescence was reversed. The fluorescense decrease is interpreted as transmembrane electrophoresis of ANS in response to a transmembrane potential.