Bromthymol blue as a pH indicator in mitochondrial suspensions

Bromothymol blue as a probe for structural changes of model membranes induced by hemoglobin

The effect of methemoglobin on the structure of model membranes composed of phosphatidylcholine and diphosphatidylglycerol (18 : 1, mol : mol) was studied with the help of pH-indicator dye bromothymol blue. The partition coefficients characterizing the dye binding to methemoglobin or model membranes were derived from the pKaalpha dependences on the protein or phospholipid concentration. The observed character of the dye partitioning in the lipid or lipid-protein systems is interpreted in terms of the traditional electrostatic approach and some modern theories of membrane electrostatics. It is assumed that methemoglobin affects the structural and physicochemical parameters of lipid-water interface.

Glynn and the conceptual development of the chemiosmotic theory: a retrospective and prospective view

The origin and evolution of the chemiosmotic theory is described particularly in relation to Peter Mitchell's application of it to model oxidative phosphorylation. Much of the deployment, development and evaluation of the theory occurred at the independent laboratory of the Glynn Research Foundation; the value and future of such an institution is discussed. The role of models mediating between theories and phenomena is analyzed with regard to the growth of knowledge of chemiosmotic systems.

Tracking of proton flow during transition from anaerobiosis to steady state. 2. Effect of cation uptake on the response of a hydrophobic membrane bound pH indicator

1. During aerobic cation uptake in liver mitochondria, the hydrophobic pH indicator bromothymol blue undergoes a multiphase response: phase 1 (rapid acidification), phase 2 (slow alkalinization), phase 3 (rapid alkalinization) and phase 4 (reacidification). 2. Titrations with ruthenium red and malonate indicate that the various phases depend on the relative rates of cation uptake and proton translocation: at high rates of cation uptake, phase 1 disappears and phases 2 and 3 are transformed in a monotonic process of alkalinization. 3. The comparison of the bromothymol blue response with the arsenazo III, 2',7'-bis(carboxyethyl)-5(6)carboxyfluorescein (BCECF) and safranine responses indicates that: (a) phase 2 (slow alkalinization) corresponds to a slow rise of matrix pH and a parallel decline of membrane potential; (b) phase 3 (rapid alkalinization) corresponds to termination of proton translocation and initiation of the processes of cation efflux and proton reuptake. All the above processes reach completion during phase 4. 4. Although bromothymol blue always behaves as a membrane-bound indicator, the extent to which it reflects the matrix or the cytosolic pH is a function of the membrane-potential-determined asymmetric distribution: in parallel with the lowering of the membrane potential, the dye chromophore is shifted from the cytosolic to the matrix side membrane layer. 5. A model is discussed which describes the behaviour of bromothymol blue as pH indicator recording the changes in membrane layers facing either the matrix or the cytosolic side. The complex response of the dye during cation uptake is due to two independent processes, one of pH change and another of dye intramembrane shift. Computer simulations of the dye response, based on the conversion of a kinetic model into an electrical network and closely reproducing the experimental observations, are reported.

Tracking of proton flow during transition from anaerobiosis to steady state in rat liver mitochondria

(1) The hydrophobic pH indicator Bromthymol blue and the hydrophilic pH indicator Phenol red have been used to follow the redox-pump-linked proton flows during transition from anaerobiosis to static head. The domains monitored by the pH indicators, whether external or internal, and the localization of the dye, whether free or membrane bound, have been identified by recording the absorbance changes following addition of nigericin or valinomycin to anaerobic or aerobic mitochondria and the effects of permeant and impermeant buffers. (2) After addition of the H+/K+ exchanger, nigericin, to anaerobic mitochondria. Phenol red and Bromthymol blue record an alkalinization and an acidification, respectively, indicating that while the hydrophilic pH indicator faces an external domain, the hydrophobic pH indicator faces, at least partly, an internal domain. The latter effect is sensitive to phosphate and to phosphate carrier inhibitors. On the other hand, addition of nigericin to aerobic mitochondria leads to an increased Bromthymol blue absorbance, which reflects an alkalinization, indicating that the pH indicator faces an external domain. The reorientation of the dye from the internal to the external domain is a function of the uncoupler concentration and thus of the membrane potential (cf. Mitchell et al. (1968) Eur. J. Biochem. 4, 9-19). (3) The amount of oxygen required for the transition from anaerobiosis to static head has been determined by following in parallel the extent of oxidation of cytochrome aa3 and the rise of delta mu H+. With succinate as substrate, 50% levels of cytochrome oxidation are obtained at 0.125 ngatom oxygen/mg and 50% of Safranine response at about 0.2 ngatom oxygen/mg. These amounts of oxygen correspond to an H+ displacement of about 0.8-1.2 ngatom/mg on the basis of the H+/O stoichiometry. It is concluded that mitochondria are in presteady state below, and in static head above, displacement of 2-3 ngatom H+/mg. This figure is very close to the original calculation of Mitchell (Mitchell, P. (1966) Biol. Rev. 41, 445-502). (4) Transition, by oxygen pulses, of EGTA-supplemented mitochondria from anaerobiosis to either presteady state or static head state results in a response of the hydrophilic pH indicator, Phenol red, which is negligible in amount and/or kinetically unrelated to the delta mu H+ rise. The fact that H+ extrusion in the bulk aqueous phase is negligible also in presteady state excludes proton cycling as an explanation. Addition of oxygen pulses to Sr2(+)-supplemented anaerobic mitochondria results in an H+ extrusion whose amount and rate is proportional to the Sr2+ concentration.(ABSTRACT TRUNCATED AT 400 WORDS)

Liposomal membrane. I. Chemical damage of liposomal membranes with functional detergent

The interaction and reaction between liposomal membrane and a functional detergent, N-hexadecyl-N-(imidazol-4-yl)methyl-N,N-dimethylammonium chloride hydroperchlorate (Im-I), have been investigated in conjunction with the leakage of bromothymol blue encapsulated as a marker in the bilayers of liposomes. Im-I carries an imidazole moiety and was expected to behave as a simple lipase model. The reaction with Im-I significantly enhanced the leakage of bromothymol blue encapsulated in the egg lecithin and dipalmitoyl phosphatidylcholine liposomes. During the course of reaction with Im-I, the formation of acyl-imidazole intermediate was clearly identified, which was certainly connected with the bromothymol blue release. From various kinetic results on bromothymol blue release and acyl-imidazole formation, it has been suggested that the bromothymol blue release from liposomal bilayer may be caused by the local and instantaneous decomposition of lipids when Im-I penetrates into the bilayer. However, it has also been demonstrated that the immediate reconstruction of liposomes retains the barrier function to protect against the further release of bromothymol blue.

Electrochemical potential of protons in vesicles reconstituted from purified, proton-translocating adenosine triphosphatase

Measurements were made of the difference in the electrochemical potential of protons (delta-mu H+) across the membrane of vesicles restituted from the ATPase complex (TF0.F1) purified from a thermophilic bacterium and P-lipids. Two fluorescent dyes, anilinonaphthalene sulfonate (ANS) and 9-aminoacridine (9AA) were used as probes for measuring the membrane potential (delta psi) and pH difference across the membrane (delta pH), respectively. In the presence of Tris buffer the maximal delta psi ans no delta pH were produced, while in the presence of the permeant anion NO-3 the maximal delta pH and a low delta psi were produced by the addition of ATP. When thATP concentration was 0.24 mm, the delta psi was 140-150 mV (positive inside) in Tris buffer, and the delta pH was 2.9-3.5 units (acidic inside) in the presence of NO-3. Addition of a saturating amount of ATP produced somewhat larger delta psi and delta pH values, and the delta -muH+attained was about 310mV. By trapping pH indicators in the vesicles during their reconstitution it was found that the pH inside the vesicles was pH 4-5 during ATP hydrolysis. The effects of energy transfer inhibitors, uncouplers, ionophores, and permeant anions on these vesicles were studied.

Anion and amine uptake and uncoupling in submitochondrial particles

1. Unlike chloroplasts, submitochondrial particles are not uncoupled by nigericin + KCl or NH4Cl. Also the uncoupling effect of lipophilic anions is largely independent of the addition of weak bases. 2. Low concentrations of permeant anions cause a shift of the steady-state energy level rather than a cycle of energy utilization. The degree of inhibition of ATP synthesis by tetraphenylboron is larger than required for the uptake of the anion. 3. Lipophilic anions such as bromthymolblue, bromcresolpurple, and 8-anilino-1-napthalene sulphonate cause a pH-independent, 50% uncoupling in submitochondrial particles at concentrations of 3, 30 and 30 muM, respectively. The passive interaction of bromthymolblue and bromcresolpurple appears as a pH-dependent distribution between two pHases. ATP causes a pH-independent slight shift in the anion distribution, with negligible anion accumulation. 4. Addition of amines to energized submitochondrial particles results in two types of effects; uptake of amines and uncoupling. While in chloroplasts amine uptake and uncoupling are closely associated, this is not the case in submitochondrial particles. The uncoupling effect is observed only with lipophilic and not with hydrophilic amines, and the degree of uncoupling increases with the lipophilicity of the amines. The amine uptake, on the other hand, is accompanied by negligible uncoupling. 5. While the uptake of amines is dependent on the presence of non-permeant anions, such as Cl-, the uncoupling effect is independent of Cl-. Furthermore the amine uncoupling is markedly enhanced by lipophilic anions. 6. The view is discussed that the uncoupling effect of lipophilic anions and lipophilic amines in submitochondrial particles is due to a catalytic energy dissipation rather than to a stoichiometry energy utilization. The molecular mechanism of uncoupling presumably involves a cycling of charges after a perturbation of the membrane structure.

Intracellular pH: measurement, control, and metabolic interrelationships

Recent work in the field of cell pH has been characterized by many developments in techniques of measurement, by increasing knowledge of the mechanism of control of cell pH, and by progress in the establishment of relationships between cell pHi and certain areas of intermediary metabolism. Though the weight of evidence is much in favor of control cell pH by active transport of H+, the situation remains somewhat unsatisfactory due to lack of a completely adequate explanation of the work of Carter's group. The heterogeneity of cell pH raises problems in the intrepretation of hydrogen ion equilibria across cell membranes and serious difficulties in correlating changes with alterations in metabolism. To put this into perspective, however, the later difficulties are no greater than many experienced with cell constituents other than hydrogen ions.90 As in other fields, knowledge must advance by making the best of the currently available methods until such time as better techniques become available.

Indicator dyes as probes of electrostatic potential changes on macromolecular surfaces

An indicator dye attached to an electrostatically charged macromolecular surface generally has a pK value (pKb') different from that of uncombined dye (pKf'). The question if changes in (pKb' - pKf'), designated as increment incrementpK, records changes in the electrostatic potential at the binding site has been examined in spectrophotometric and binding experiments, using the interaction of Chlorophenol Red and Phenol Red with human serum albumin and cationic micelles as examples. (1) In serum albumin solutions increment incrementpK is decreased by a reduction of pH. The decrease is correlated with the increase in positive charges on the protein molecule, and the response is attenuated by high ionic strength in accordance with electrostatic theory. (2) Opposite changes in binding affinity to serum albumin and increment incrementpK as a function of pH are observed; the binding of basic (bivalent anion) dye is more susceptible to a change in pH than in the acidic (univalent anion) form. (3) Preferential uptake of the basic as compared to the acidic form of dye is observed by binding to cetyltrimethylammonium chloride and cetylpyridinium chloride micelles (mu equals 0.033, [Cl-] equals 0.033 M). An increase in the ionic strength is accompanied by a positive value of increment incrementpK. The results are consonant with the view that the observed increment incrementpK values reflect changes in the electrostatic potential at the binding site with consequently little, if any, effect on the intrinsic pK. The extension of the method to measure changes in the electrostatic potential at binding sites on cell membranes is briefly discussed.

The inhibition by bromothymol blue of anion translocation across the mitochondrial membrane

1. In rat liver mitochondria bromothymol blue inhibited the exchange of [14C]succinate for succinate, malonate, L-malate and inorganic phosphate; the [14C]citrate/citrate and [14C]citrate/malate exchange reactions and the phosphate/hydroxyl exchange were also inhibited by this dye. The inhibition of the rate of succinate, citrate and phosphate uptake by bromothymol blue is found to be competitive. 2. The degree of inhibition by bromothymol blue of the ]14C]succinate/malonate exchange reaction was pH dependent. It has been shown that the inhibition increased linearly while the pH was increased from 6.0 to 8.2. However, the binding rate of bromothymol blue to the mitochondria decreased with the rising pH of the medium. It is concluded that the binding of acidic bromothymol blue was not essential for the inhibitory effect. 3. Other sulfonephthalein derivatives also inhibited [14C]succinate/malonate exchange reaction. At pH 7.2 the relative order of the strength of the inhibitory action of the sulfonephthalein compounds tested was: thymol blue greater than bronocresol green greater than bromothymol blue greater than phenol red greater than bromocresol purple. The results do not indicate any correlation between the pK values of pH values of pH indicators and their extents of inhibition. 4. It is suggested that the negatively charged bromothymol blue interacts with the positively charged centers of the anion carrier systems causing inhibition of membrane permeability for anions.

Relationship of a proton gradient to the active transport of proline with membrane vesicles from Mycobacterium phlei

Electron transport particles prepared from Mycobacterium phlei were depleted of bound coupling factors by washing with water in the absence of inorganic ions. The depleted electron transport particles were void of latent ATPase activity and were capable of oxidation, but were unable to support coupled phosphorylation. Nevertheless, the depleted electron transport particles were capable of substrate-induced active transport of proline. Changes in pH in response to substrate oxidation were measured in normal and depleted electron particles with bromthymol blue. A bromthymol blue response upon substrate oxidation was not observed with depleted electron transport particles. The level of oxidative phosphorylation with succinate or NADH oxidation was not reduced in the presence of proline, and proline did not have an effect upon the proton gradients formed by the oxidation of either succinate or NADH.

Enzyme and membrane conformation in biochemical control

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