Amphiphilic Amines Research Articles

Enabling direct seawater electrolysis by redox-inactive amphiphilic amines via chloride sequestration

Sustainable hydrogen production requires large amounts of treated freshwater and precious metals. Direct electrolysis of seawater without additional electrolytes can be a practical approach to address these limitations, however, it usually suffers from kinetically favored chlorine evolution reaction (CER), which is detrimental to an electrolysis system. We report that organocatalytic amphiphilic diamines play a crucial role in preventing the generation of chlorine gas. The feasibility of direct seawater electrolysis was demonstrated with pH-responsive organic amines, which can self-assemble under neutral and acidic conditions. Electrochemical analysis of our electrolysis in saline solutions revealed that (electro)chemical stability of amphiphilic diamines was responsible for preventing CER and hypochlorite formation. Our findings may have significant implications for the chemical industry and energy sectors as the world transitions towards renewable energy sources.

Direct Monitoring of Molecular Events at the Surface: One-Step Access to Flexibly Stable Colloidal Ag Nanoparticles.

Design, control, and direct characterization of surface properties are prerequisites to all the practical applications of nanoparticles. Since stable and homogeneous colloidal conditions are required for most applications, the amenability of nanoparticles to in-solution processing must also be addressed. Herein, we demonstrate that solution 1H NMR spectroscopy is an effective tool for direct monitoring of the production of Ag nanoparticles. The production consists of two stages, complexation and reduction, which are both clearly observed by 1H NMR spectroscopy. Design and synthesis of a series of amphiphilic amines have led to the one-step production of "flexibly" stable colloidal Ag nanoparticles, which form clear stable brown solutions in a wide range of solvents.

Preparation and Evaluation of a Novel Class of Amphiphilic Amines as Antitumor Agents and Nanocarriers for Bioactive Molecules

PurposeWe describe a novel class of antitumor amphiphilic amines (RCn) based on a tricyclic amine hydrophilic head and a hydrophobic linear alkyl tail of variable length.MethodsWe tested the lead compound, RC16, for cytotoxicity and mechanism of cell death in several cancer cell lines, anti tumor efficacy in mouse tumor models, and ability to encapsulate chemotherapy drugs.ResultsThese compounds displayed strong cytotoxic activity against cell lines derived from both pediatric and adult cancers. The IC50 of the lead compound, RC16, for normal cells including human keratinocytes, human fibroblasts and human umbilical vein endothelial cells was tenfold higher than for tumor cells. RC16 exhibited significant antitumor effects in vivo using several human xenografts and a metastatic model of murine neuroblastoma by both intravenous and oral administration routes. The amphiphilic character of RC16 triggered a spontaneous molecular self-assembling in water with formation of micelles allowing complexation of Doxorubicin, Etoposide and Paclitaxel. These micelles significantly improved the in vitro antitumor activity of these drugs as the enhancement of their aqueous solubility also improved their biologic availability.ConclusionsRC16 and related amphiphilic amines may be useful as a novel cancer treatment.Electronic supplementary materialThe online version of this article (doi:10.1007/s11095-016-1999-9) contains supplementary material, which is available to authorized users.

Molecular Simulation Study of the Early Stages of Formation of Bioinspired Mesoporous Silica Materials

The use of bioinspired templates, such as polyamines and polypeptides, could lead to significant improvements in the synthesis conditions under which mesoporous materials are traditionally produced, removing the need for strong pH as well as high temperature or pressure. In this work, we perform atomistic molecular dynamics simulations of 1,12-diaminododecane surfactants, in water and in the presence of silica monomers, to investigate the early stages of synthesis of one of the first examples of bioinspired silica materials. Different surfactant concentrations and pH were considered, clarifying the influence of the charge state of the molecules on the self-assembly process. We show that the amphiphilic amines form stable lamellar structures at equilibrium in the range from intermediate to high pH values. In a later stage, when silica species are added to the system, our results reveal that, in the same range of pH, silicates strongly adsorb around these aggregates at the interface with water. This causes a considerable modification of the curvature of the layer, which suggests a tendency for the system to evolve from a lamellar phase to the formation of vesicle structures. Furthermore, we show that silica monomers are able to penetrate the layer spontaneously when defects are created as a result of surfactants' head-to-head repulsion. These findings are in agreement with experimental observations and support the pillaring mechanism postulated for this class of materials. However, our simulations indicate that the aggregation process is driven by charge matching between surfactant heads and silica monomers rather than by hydrogen bond interactions between neutral species, as had been previously hypothesized.

Phospholipase C activation by anesthetics decreases membrane-cytoskeleton adhesion.

Many different amphiphilic compounds cause an increase in the fluid-phase endocytosis rates of cells in parallel with a decrease in membrane-cytoskeleton adhesion. These compounds, however, do not share a common chemical structure, which leaves the mechanism and even site of action unknown. One possible mechanism of action is through an alteration of inositol lipid metabolism by modifying the cytoplasmic surface of the plasma membrane bilayer. By comparing permeable amphiphilic amines used as local anesthetics with their impermeable analogs, we find that access to the cytoplasmic surface is necessary to increase endocytosis rate and decrease membrane-cytoskeleton adhesion. In parallel, we find that the level of phosphatidylinositol 4,5-bisphosphate (PIP(2)) in the plasma membrane is decreased and cytoplasmic Ca(2+) is increased only by permeable amines. The time course of both the decrease in plasma membrane PIP(2) and the rise in Ca(2+) parallels the decrease in cytoskeleton-membrane adhesion. Inositol labeling shows that phosphatidylinositol-4-phosphate levels are increased by the permeable anesthetics, indicating that lipid turnover is increased. Consistent with previous observations, phospholipase C (PLC) inhibitors block anesthetic effects on the PIP(2) and cytoplasmic Ca(2+) levels, as well as the drop in adhesion. Therefore, we suggest that PLC activity is increased by amine anesthetics at the cytoplasmic surface of the plasma membrane, which results in a decrease in membrane-cytoskeleton adhesion.

Effects of Amphiphilic Amines on Moisture Characteristics of Alluvial and Volcanic Soils

If organic matter (OM) has amphiphilicity, the properties of hydration of the OM‐coated soil particles would vary drastically in dry conditions. Therefore, soil‐moisture characteristics within the relatively low water potential should be understood in relation to the conformation of the sorbed amphiphilic OM. In the present study, the effects of amphiphilic behavior of OM on the moisture characteristics of alluvial soil (AS) and volcanic soil (VS) were investigated using three simple amphiphilic amines. The psychrometry of AS showed the decrease of sorbed water around 1.8 nm of statistical thickness because of the sorption of hexadecyltrimethyl ammonium (HDTMA). Fourier transform infrared spectroscopy (FTIR) of soils showed an increase in the wavenumber of the antisymmetric stretching of ‐OH and ‐CH2, suggesting the formation of hydrophobic outer surfaces by n–hexadecyl function. The peaks in the ‐CH2 rocking band suggest that the HDTMA sorbed at AS had the residual amorphous moieties. In the case of VS–HDTMA, the peak was hidden by a broad peak due to hydrated aluminosilicates in VS. These findings imply that the amorphous moieties of HDTMA sorbed at both soils were affected by residual water in the air dried samples. According to the clay mineralogy of the soils, the greater hydrophobicity in AS–HDTMA was attributed to intercalation of HDTMA into the expansible phyllosilicates in AS. In contrast, the relatively moderate hydrophobicity in VS–HDTMA indicated that the hydrophilic micropores (D < 2 nm) in VS restrict the sorption of HDTMA but enable it to exchange water.

Active transport inhibition in rat small intestine by amphiphilic amines: an In Vitro study with various local anaesthetics

In the present investigation with rings of everted rat small intestine, amphiphilic amines such as local anaesthetics (e.g. lidocaine, procaine, tolycaine) were employed to study their effects on intestinal absorption of methyl α- d-glucoside, l-leucine, d-fructose, and 2-deoxy- d-glucose. All the amphiphilic amines tested, except for benzocaine, significantly inhibited Na +-dependent active uptake of methyl α- d-glucoside and l-leucine while leaving uptake of d-fructose (facilitated diffusion) and 2-deoxy- d-glucose (passive diffusion) unaffected. Increasing concentrations of lidocaine in the incubation medium inhibited the uptake of methyl α- d-glucoside ( ic 50 ∼3.5 mmol/L) and l-leucine ( ic 50 ∼6 mmol/L) in a dose-dependent manner. Complete reversibility of the inhibitory effect could only be achieved at short-term incubations (≤2 min) and low lidocaine concentrations (≤3 mmol/L), otherwise inhibition became partially irreversible. Uptake kinetics of methyl α- d-glucoside and l-leucine in the presence of lidocaine revealed a significant increase in the apparent Michaelis constant, leaving the maximal transport capacity essentially unaltered. Reducing the Na + concentration in the incubation medium aggravated inhibition by lidocaine of the uptake of methyl α- d-glucoside. Analysis of the inhibition kinetics by Dixon plots revealed a competitive interaction between Na + and the amphiphiles. However, phlorizin binding was not affected by lidocaine. Changing the pH of the incubation medium from 5.6 to 8.0 increased the inhibitory effect of the amphiphiles, which indicated that the non-ionised and, thus, more lipophilic form participates in the mechanism of inhibition. However, benzocaine, a rather lipophilic local anaesthetic with no aliphatic amino group, did not impair active uptake of methyl α- d-glucoside. Whether the amphiphilic amines act by their partition into the membrane matrix or directly interact with sodium binding sites remains to be elucidated, however.

CHARACTERIZATION OF THE PULMONARY N-ETHYLMALEIMIDE-INSENSITIVE PHOSPHATIDATE PHOSPHOHYDROLASE

Phosphatidate phosphohydrolase (PAPase) is a key enzyme involved in glycerolipid synthesis where it converts phosphatidic acid to diacylglycerol. Previous studies performed in lung have demonstrated the existence of 2 different forms of PAPases, namely PAP-1 and PAP-2. The former pulmonary Mg+ 2- dependent enzyme is N-ethylmaleimide (NEM)-sensitive, heat labile, and is involved in phospholipid biosynthesis. However, the function of the latter lung isozyme is unknown. PAP-2 activity was selectively assayed using NEM in the absence of Mg+2. Studies employing this assay and adult rat lung microsomal preparations demonstrated that PAP-2 activity was inhibited by amphiphilic amines, sphingoid bases, products of the PAP-2 reaction (monoacylglycerol\\[MAG] and diacylglycerol \\[DAG]), and substrate analogs such as lysophosphatidic acid (lyso-PA), ceramide-1-phosphate, and to a lesser extent, sphingosine-1-phosphate. Purified lung plasma membranes, prepared using discontinuous sucrose and Percoll gradients, showed that PAP-2 activity was enriched 6.9 +/- 1.6-fold over the whole homogenate and was between the enrichment for plasma membrane markers, 5'-nucleotidase (14.7 +/- 0.3) and Na+, K+- ATPase (4.0 +/- 0.2). Both phosphatidic acid and lysophosphatidic acid were good substrates for PAP-2 activity in this purified plasma membrane fraction. In contrast, sphingosine-1-phosphate was a relatively poor substrate. PAP-2 activity was slightly enriched in isolated type II cells and low in isolated rat lung broblasts. This study shows lung contains PAP-2 activity in plasma membranes and type II cells where it could play a role in signal transduction.

Different modes of inhibition by adamantane amine derivatives and natural polyamines of the functionally reconstituted influenza virus M2 proton channel protein.

The influenza virus M2 protein, target of the antiviral drugs amantadine and rimantadine, forms a proton channel which functions during virus uncoating and maturation by modifying the pH in virions as well as in trans-Golgi vesicles. We studied the influence of different ionic gradients on the inhibition of the proton translocation activity of isolated, baculovirus-expressed M2 protein reconstituted into liposomes. Two distinct patterns of inhibition were observed. A group of amphiphilic amines including amantadine, cyclooctylamine and rimantadine inhibited M2 effectively in the presence of physiological Na+ concentrations. The 10-fold greater activity of rimantadine over amantadine and the 100-fold stronger effect of cyclooctylamine compared to cyclopentylamine matched the relative activities in influenza virus-infected cells. A completely different inhibitory pattern emerged for the polyamines spermine, spermidine and putrescine. Polyamines have recently been identified as the 'intrinsic' rectifiers of a class of potassium channels and shown to interact with acidic amino acid residues lining and flanking the channel pore. In the presence of a physiological Na+/K+ gradient their minimal inhibitory concentrations for influenza virus M2 protein were 100, 400 and 500 microM, polyamine levels reported to exist in oocytes. In conditions depleted for Na+, polyamines inhibited M2 at concentrations two to three orders of magnitude lower. The data suggest that influenza virus M2 protein possesses a binding site for polyamines, distinct from the amantadine binding site, which is normally masked by Na+ and which could be targeted by selective antiviral inhibitors.

Purification and characterization of N-ethylmaleimide-insensitive phosphatidic acid phosphohydrolase (PAP2) from rat liver.

N-Ethylmaleimide-insensitive phosphatidic acid phosphohydrolase (PAP; EC 3.1.3.4) was purified 5900-fold from rat liver. The enzyme was solubilized from membranes with octylglucoside, fractionated with (NH4)2SO4, and purified in the presence of Triton X-100 by chromatography on Sephacryl S300, hydroxyapatite, heparin-Sepharose and Affi-Gel Blue. Silver-stained SDS/PAGE indicated that the enzyme was an 83 kDa polypeptide. Sephacryl S-300 gel filtration also produced a second peak of enzyme activity, which was eluted from all of the chromatography columns at a different position from the purified enzyme. SDS/PAGE indicated that it contained three polypeptides (83 kDa, 54 kDa and 34 kDa), and gel filtration suggested that it was not an aggregate of the purified enzyme. Both forms were sensitive to inhibition by amphiphilic amines, Mn2+ and Zn2+, but not by N-ethylmaleimide. Purified PAP required detergent for activity, but was not activated by Mg2+, fatty acids or phospholipids. The enzyme was able to dephosphorylate lysophosphatidic acid or phosphatidic acid, and was inhibited by diacylglycerol and monoacylglycerol. No evidence was obtained for regulation of PAP by reversible phosphorylation.

Intracellular trafficking of dolichol: on the presence of dolichol transfer activity in bovine liver supernatant.

A protein catalyzing dolichol transfer between membranes has been purified from bovine liver up to 600-fold by acid precipitation, ammonium sulfate precipitation, ion-exchange chromatography and hydrophobic interaction chromatography. The protein displays a relative molecular mass of 15000 on SDS-gel electrophoresis. Kinetics as well as the influence of a series of effectors were studied. The transfer activity is inhibited by sphingomyelin, sulfhydryl groups and cationic amphiphilic amines with a bulky heterocyclic aromatic function. High salt concentration decreases the transfer efficiency. Transfer of dolichol between vesicles and mitochondria is not affected by the presence of moderate amounts of cholesterol in the donor vesicles. The overall characteristics of dolichol transfer activity are discussed in comparison to these of other lipid transfer proteins.

On the regulation of Na +/H + and K +/H + antiport in yeast mitochondria: Evidence for the absence of an Na +-selective Na +/H + antiporter

Unlike mammalian mitochondria, yeast mitochondria swell spontaneously in both NaOAc and KOAc. This swelling reflects the activity of an electroneutral cation/H + antiport pathway. Transport of neither salt is stimulated by depletion of endogenous divalent cations; however, it can be inhibited by addition of exogenous divalent cations (Mg 2+ IC 50 = 2.08 mM, Ca 2+ IC 50 = 0.82 mM). Transport of both Na + and K + can be completely inhibited by the amphiphilic amines propranolol (IC 50 = 71 μM) and quinine (IC 50 = 199 μM) with indistinguishable IC 50 values. Dicyclohexylcarbodiimide inhibits with a second-order rate constant of 1.6·10 −4 (nmol DCCD/mg) −1 min −1 at 0°C; however, with both Na + and K + inhibition reaches a maximum of about 46%. The remaining transport can still be inhibited by propranolol. Transport of both cations is sensitive to pH; yielding linear Hill plots and Dixon plots with a pIC 50 value of 7.7 for both Na + and K +. These properties are qualitatively the same as those of the non-selective K +/H + antiporter of mammalian mitochondria. However, the remarkable similarity between the data obtained in Na + and K + media suggests that an antiporter akin to the Na +-selective Na +/H + antiporter of mammalian mitochondria, which is inhibited by none of these agents, is absent in yeast. In an attempt to reveal the activity of a propranolol-insensitive Na +-selective antiporter, we compared the rates of Na +/H + and K +/H + antiport in the presence of sufficient propranolol to block the K +/H + antiporter. Between pH 4.6 and 8.8 no difference could be detected. Consequently, we conclude that yeast mitochondria lack the typical Na +-selective Na +/H + antiporter of mammalian mitochondria.

On the mechanism by which bupivacaine conducts protons across the membranes of mitochondria and liposomes.

Bupivacaine and etidocaine possess the remarkable property of stimulating mitochondrial respiration to levels comparable with those observed with classical anionic protonophores (Dabadie, P., Bendriss, P., Erny, P., and Mazat, J.P. (1987) FEBS Lett. 226, 77-82). We show that these amphiphilic amines conduct protons across the membranes of mitochondria and liposomes and stimulate respiration by a true protonophoretic mechanism. The kinetics of drug-induced H+ flux exhibited integer Hill coefficients that were greater than two under all conditions, suggesting that multimers are required for H+ transport. When the energy barrier for ion transport was lowered in mitochondria, by increasing the membrane potential, or in liposomes, by adding phloretin, the Hill coefficients decreased to lower integer numbers. Protonophoretic activity depended exclusively on medium concentration of free base, leading us to conclude that bupivacaine and etidocaine conduct protons as associated, intramembrane multimers of the free base. Bupivacaine-induced H+ leak was ohmic rather than nonohmic, as would be expected of a mobile charged carrier. This kinetic behavior seems improbable for a multimeric mobile carrier mechanism and suggests a channel mechanism, in which ohmicity results from splitting of the energy barrier by energy wells along the transport pathway (Garlid, K. D., Beavis, A. D., and Ratkje, S. K. (1989) Biochim. Biophys. Acta 976, 109-120). We hypothesize that bupivacaine and etidocaine act by a novel "flickering channel" mechanism, in which transient linear complexes of free base molecules provide weak binding sites (energy wells) for protons within lipid bilayer membranes.

Effects of sphingosine, albumin and unsaturated fatty acids on the activation and translocation of phosphatidate phosphohydrolases in rat hepatocytes

The activities of two phosphatidate phosphohydrolases were measured in cultured rat hepatocytes incubated with 0.1 mM albumin. The activity, which is inhibited by N-ethylmaleimide (PAP-1) is located in the cytosolic and membrane fractions. PAP-1 activity is stimulated by Mg 2+ and it can be translocated from the cytosol to the membranes by relatively low (0.5–1 mM) concentrations of fatty acids. In addition, higher concentrations (1–3 mM) of fatty acids cause an increase in the total PAP-1 activity. Translocation of PAP-1 activity in the hepatocytes is preferentially promoted by unsaturated fatty acids (C 18:1, C 18:2, C 18:3, C 20:4 and C 20:5), rather than by saturated acids (C 14:0, C 16:0, C 18:0). Increasing the extracellular concentration of albumin from 30 μM to 1 mM displaces PAP-1 activity from the membrane fraction. Sphingosine, but not staurosporine, can inhibit the redistribution of PAP-1 activity induced by oleate. The amphiphilic amines, sphingosine, chlorpromazine and propranolol, also decrease membrane-bound PAP-1 activity in the absence of fatty acids, but they do not alter, significantly, the activity of the cytosolic PAP-1. In the presence of 1 mM oleate, sphingosine, chlorpromazine and propranolol decrease the translocation of PAP-1 from the cytosol to the membranes. The phosphohydrolase activity, which is insensitive to N-ethylmaleimide (PAP-2), is specifically located in the plasma membrane (Jamal, Z., Martin, A., Gomez-Muñoz, A. and Brindley, D.N. (1991) J. Biol. Chem. 266, 2988–2996) and it is not stimulated by Mg 2+. Saturated fatty acids, albumin, sphingosine and propranolol have no significant effects on PAP-2 activity. However, chlorpromazine decreases PAP-2 activity by about 14%. Linolenate, arachidonate and eicosapentaenoate at 1 mM also produced small (7–10%) decreases in PAP-2 activity. It is proposed that both PAP-1 and PAP-2 activities may be involved in signal transduction, although the main function of PAP-1 seems to be involved in the synthesis of glycerolipids.

K +/H + exchange in yeast mitochondria: sensitivity to inhibitors, solubilization and reconstitution of the activity in proteoliposomes

The K +/H + exchange activity of the inner mitochondrial membrane was investigated in the yeast Saccharomyces cerevisiae. Swelling experiments in potassium acetate indicated that the K +/H + exchange was active without any additional treatment after the mitochondria isolation, such as a Mg 2+ depletion. As in mammalian mitochondria, the activity of yeast mitochondria was stimulated by increasing pH and was inhibited by the amphiphilic amines quinine and propanolol and by the car☐yl reagent dicyclohexylcarbodiimide. However, the activity was poorly inhibited by Mg 2+ and consequently was only slightly stimulated by the Mg 2+/H + exchanger A23187. On the other hand, Zn 2+ was very efficient for inhibiting the exchange and consequently the activity was strongly stimulated by the permanent metal-chelator o-phenanthroline. The [ 86Rb]Rb + accumulation in mitochondria and mitoplasts was only partially inhibited by quinine and propanolol suggesting that part of the accumulation monitored under these conditions was due to cation leak through the inner membrane together with adsorption on the membrane. The DCCD-sensitive activity could be reconstituted from mitochondria and from mitoplasts solubilized with Triton X-100; this activity, measured by [ 86Rb]Rb + accumulation, was quinine- and propranolol-sensitive. A spectrophotometric method, based on the capacity of negatively charged proteoliposomes to swell, was then developed in order to continuously follow the reconstituted activity.

Triorganotins inhibit the mitochondrial inner membrane anion channel.

The inner membrane of liver and heart mitochondria possesses an anion uniport pathway, known as the inner membrane anion channel (IMAC). IMAC is inhibited by matrix Mg2+, matrix H+, N,N'-dicyclohexycarbodiimide, mercurials and amphiphilic amines such as propranolol. Most of these agents react with a number of different mitochondrial proteins and, therefore, more selective inhibitors have been sought. In this paper, we report the discovery of a new class of inhibitors, triorganotin compounds, which block IMAC completely. One of the most potent, tributyltin (TBT) inhibits malonate uniport via IMAC 95% at 0.9 nmol/mg. The only other mitochondrial protein reported to react with triorganotins, the F1F0ATPase, is inhibited by about 0.75 nmol/mg. The potency of inhibition of IMAC increases with hydrophobicity in the sequence trimethyltin much less than triethyltin much less than tripropyltin less than triphenyltin less than tributyltin; which suggests that the binding site is accessible from the lipid bilayer. It has long been established that triorganotins are anionophores able to catalyze Cl-/OH- exchange; however, TBT is able to inhibit Cl- and NO3- transport via IMAC at doses below those required to catalyze rapid rates of Cl-/OH- exchange. Consistent with previous reports, the data indicate that about 0.8 nmol of TBT per mg of mitochondrial protein is tightly bound and not available to mediate Cl-/OH- exchange. We have also shown that the mercurials, p-chloromercuribenzene sulfonate and mersalyl, which only partially inhibit Cl- and NO3- transport can increase the IC50 for TBT 10-fold. This effect appears to result from a reaction at a previously unidentified mercurial reactive site. The inhibitory dose is also increased by raising the pH and inhibition by TBT can be reversed by S2- and dithiols but not by monothiols.

Evidence for two distinct chloride uniport pathways in brown adipose tissue mitochondria

Chloride permeability of the inner membrane of brown adipose tissue mitochondria was analyzed by monitoring mitochondrial swelling in KCl salts in the presence of K+ ionophores. The results indicate that the high anion conductance observed in these mitochondria is due to the presence of two separate pathways: 1) a Cl-conducting pathway that is inhibited by guanosine 5'-diphosphate (GDP) but neither by N,N'-dicyclohexylcarbodiimide (DCCD) nor by amphiphilic amines and that is found uniquely in brown adipose tissue mitochondria and 2) an inner membrane anion uniport channel that is inhibited both by DCCD and by amphiphilic amines but not by GDP and that is opened either by depletion of matrix Mg2+ or by alkalinization of the matrix.

Sodium/proton antiporters in the mitochondrial inner membrane.

The two mitochondrial Na+/H+ antiporters differ in several important respects, and the most physiologically significant of these may be their differences in regulation. The Mg2+-dependent Na+/H+ antiporter controls mitochondrial volume in a dangerous, high-K+ environment. To play this vital role, this porter must always lie poised far from K+/H+ equilibrium; i.e., it must be under dynamic regulation, as proposed in the Mg2+ carrier-brake hypothesis (7). Being regulated, it is not necessary for this antiporter to be cation-selective, since all electroneutral cation movements will be followed by redistributions of anions and water. On the other hand, there is no indication at present that the Mg2+-independent Na+/H+ antiporter is regulated. This transporter is therefore required to exhibit high discrimination against K+ in order to prevent the collapse of matrix volume dueto uncontrolled loss of K+ salts and water (4). Do the properties of the mitochondrial Na+/H+ antiporters help us in any way to understand the plasmalemmal Na+/H+ antiporters? I believe they do, if we allow that there are a limited number of ways in which nature constructs such porters. The difference in cation selectivities very likely reflects a fundamental structural difference between the two mitochondrial antiporters, and this difference appears to be mirrored in two types of plasmalemmal Na+/H+ antiporters. Thus, the Mg2+-independent Na+/H+ antiporter resembles the renal tubular Na+/H+ antiporter in its discrimination against K+ and its competitive inhibition by Li+. On the other hand, the Mg2+-dependent Na+/H+ antiporter resembles a cardiac sarcolemmal Na+/H+ antiporter which transports all alkali cations, including Na+ and K+, and which is inhibited by DCCD and amphiphilic amines (S. Kakar, A. Askari and K. Garlid, in preparation). The existence of the latter class of antiporter in plasmalemma may seem unlikely at first glance, since it would tend to catalyze Na+/K+ exchange and dissipate the effects of the Na+,K+-ATPase. Nevertheless, a sound design principle would be followed if the cell, like mitochondria, were to regulate volume by governing a passive back-flow process rather than an active transport process. In conclusion, it seems premature to conclude that plasma membranes contain only one type of Na+/H+ antiporter. Nor does it seem likely that there is an unlimited variety of such transporters. I propose as a working hypothesis that antiporters from both mitochondria and plasmalemma may be separated into two classes: Na+-selective and non-Na+-selective.(ABSTRACT TRUNCATED AT 400 WORDS)

Phosphatidylinositol transfer proteins: Structure, catalytic activity, and physiological function

Among the diverse lipid transfer proteins which are found in tissues and biological fluids are those which exhibit a specificity toward phosphatidylinositol and phosphatidylcholine, with a preference for the former. Phosphatidylinositol transfer proteins (PI-TPs) have been purified from several eukaryotic sources; those present in bovine brain and heart have been extensively studied. This review examines the tissue distribution of PI-TPs and the means by which transfer activity is measured using natural and artificial membranes. The interaction of these proteins with lipid monolayers and bilayers is discussed in terms of phospholipid fatty acyl and polar head group compositions. The inhibition of transfer activity by sulfhydryl agents and amphiphilic amines is summarized. The metabolism of the phosphoinositides is considered and a role for PI-TPs is proposed.

Fluorescence studies of the binding of amphiphilic amines with phospholipids.

The binding characteristics of several amine drugs with dispersed phospholipids (phosphatidylcholine, phosphatidylserine, and phosphatidylglycerol) have been studied using the fluorometric method and 1-anilino-8-naphthalene sulfonate and 1,6 diphenyl-1,3,5-hexatriene as fluorescence probes. The results show that amphiphilic amines, such as chlorphentermine, interact with phospholipids via both ionic and hydrophobic forces. The ionic interaction, which occurs between the protonated amine group of the drug and the phosphate oxygen of the lipid, changes the amphiphilic characteristics of the lipid by reducing the number of negative charges on the lipid vesicles, and inhibits the Ca2+-dependent lipid hydrolysis by blocking the Ca2+ binding sites on the lipid vesicles. The hydrophobic interaction, which involves the nonpolar moieties of the drug and the lipid, is of primary importance to the overall drug-lipid binding stability. Drugs without a strong hydrophobic moiety, such as dopamine, do not interact with phospholipids.