Membranes and Transport

Reconstitution of Escherichia coli membrane vesicles with D-amino acid dehydrogenase

When purified D-amino acid dehydrogenase [Olsiewski, P. J., Kaczorowski, G. J., & Walsh, C. T. (1980) J. Biol. Chem. 255, 4487] is incubated with right-side-out membrane vesicles from Escherichia coli, the enzyme binds to the membrane in a time- and concentration-dependent manner. As a result, the vesicles acquire the ability to oxidize D-alanine and catalyze D-alanine-dependent active transport. Similarly, incubation of D-amino acid dehydrogenase with inside-out vesicles results in binding of enzyme and D-alanine oxidase activity. Antibody inhibition studies indicate that the enzyme is bound exclusively to the inner cytoplasmic surface of the membrane in native vesicles (i.e., membrane vesicles prepared from cells induced for D-amino acid dehydrogenase). In contrast, similar studies with reconstituted vesicles demonstrate that enzyme binds to the surface exposed to the medium regardless of the orientation of the membrane. Thus, enzyme bound to right-side-out vesicles is located on the opposite side of the membrane from where it is normally found. Remarkably, in the presence of D-alanine, reconstituted right-side-out and inside-out vesicles generate electrochemical proton gradients of similar magnitude but opposite polarity, indicating that enzyme bound to either surface of the membrane is physiologically functional. The results suggest that vectorial proton translocation via the respiratory chain occurs at a point distal to the site where electrons enter the respiratory chain from the primary dehydrogenase, a conclusion that is inconsistent with the notion that the dehydrogenase forms part of a proton-translocating loop.

Hypersensitivity to Hg2+ and hyperbinding activity associated with cloned fragments of the mercurial resistance operon of plasmid NR1

The region of plasmid NR1 concerned with resistance to Hg2+ and organomercurials consists of sequences found on restriction endonuclease fragments EcoRI-H and EcoRI-I. When both fragments were cloned together into a derivative of plasmid ColE1, the hybrid plasmid conferred properties indistinguishable from those of the parental plasmid, NR1: resistance to Hg2+ and to the organomercurials merbromin and fluoresceinmercuric acetate and the inducible synthesis of the enzyme mercuric reductase. When fragment EcoRI-I was cloned into plasmid ColE1, cells containing the plasmid was as sensitive to Hg2+ and organomercurials as plasmidless strains. When fragment EcoRI-H was cloned into ColE1, cells with the hybrid plasmid were hypersensitive to Hg2+ and organomercurials. This hypersensitivity was inducible by prior exposure to low, subtoxic Hg2+ or merbromin levels. It was associated with an inducible hyperbinding activity attributed to a gene governing Hg2+ uptake and found on fragment EcoRI-H (which contains the proximal portion of a mercuric resistance [mer] operon).

Active transport by membrane vesicles from anaerobically grown Escherichia coli energized by electron transfer to ferricyanide and chlorate

Active transport of amino acids by membrane vesicles from Escherichia coli, grown anaerobically on glucose in the presence of nitrate, can be energized under anaerobic conditions by electron transfer in the nitrate respiration system with formate as electron donor and nitrate as acceptor. A high rate of amino acid transport is also obtained under anaerobic conditions by electron transfer from formate to the nitrate analogue chlorate or to the membrane-impermeable electron acceptor ferricyanide. Electron transfer from formate to nitrate results in the generation of an electrical potential as is indicated by the uptake of the lipophilic cation triphenylmethylphosphonium. Ferricyanide accpets electrons from at least two sites of the nitrate respiration system. One of these sites appears to be nitrate reductase, because cytochrome b, reduced by formate, is completely reoxidized by ferricyanide and glutamate transport energized by formate plus ferricyanide and formate plus nitrate are affected by the same electron transfer inhibitors. A second site of electron transfer to ferricyanide appears to be located prior to nitrate reductase in the nitrate respiration system, since formate is oxidized at a higher rate in the presence of ferricyanide than with nitrate while formate/ferricyanide energizes transport of amino acids at a lower rate than formate/nitrate. Moreover, electron transfer inhibitors block electron transfer from formate to nitrate to a significantly higher extent than from formate to ferricyanide. The effects of irradiation of the membrane vesicles with near ultra-violet light suggest that quinones play an essential role in the electron transfer from formate to nitrate or ferricyanide. Irradiation blocks completely formate-dependent nitrate and ferricyanide reduction and active transport driven by formate/nitrate and formate/ferricyanide, but has hardly any effect on the activity of formate dehydrogenase and on ascorbate/phenazine methosulphate/oxygen-driven transport. Similar effects of ferricyanide have been observed in membrane vesicles from E. coli, grown anaerobically in the presence of fumarate. In these membrane vesicles a high rate of lactose and triphenylmethylphosphonium uptake under anaerobic conditions is obtained by electron transfer from glycerol 1-phosphate to fumarate and also to ferricyanide and evidence has been presented for the involvement of cytochromes in these electron transfers.

Reconstitution of reduced nicotinamide adenine dinucleotide oxidase activity with menadione in membrane vesicles from the menaquinone-deficient Bacillus subtilis aro D. Relation between electron transfer and active transport

Membrane vesicles from the menaquinone-deficient Bacillus subtilis aro D contain a low content of menaquinone and consequently oxidaze reduced nicotinamide adenine dinucleotide (NADH) at low rate. Supplementation of the membrane vesicles suspension with the menaquinone-analogue menadione, results in an incorporation of menadione in the membranes. The incorporated menadione increases with the external menadione concentration up to a maximum of 7 nmol of menadione bound per mg membrane protein. The NADH oxidase activity of the membrane vesicles increases linearly with the menadione content and a 35-fold stimulation is obtained in fully reconstituted membrane vesicles; this maximal NADH oxidase activity is about two-fold higher than the NADH oxidase activity in membrane vesicles from wild-type B.subtilis W23. Supplementation of membrane vesicles from B.subtilis W23 with menadione also results in a stimulation of the NADH oxidase activity but only a stimulation of 1.6-fold is maximally obtained. The NADH oxidase activities in reconstituted B.subtilis aro D and B.subtilis W23 membrane vesicles are similarly affected by respiratory chain inhibitors, indicating that menadione occupies physiological sites of menaquinone. NADH and the non-physiological electron donor ascorbate + phenazine methosulphate are the best energy sources for active amino acid transport in membrane vesicles from B.subtilis W23. Membrane vesicles from B.subtilis aro D accumulate amino acids in the presence of acorbate + phenazine methosulphate, but not with NADH. However, membrane vesicles from this mutant, reconstituted with menadione, demonstrate NADH-driven transport activity. This activity increases linearly with the NADH oxidase activity, but maximal transprt activities are reached under conditions where the NADH oxidase activity is not yet maximal. These results indicate that the rate of energy supply is the limiting factor for transport at low NADH oxidase activities and that the transport system itself becomes the limiting factor for transport at low NADH oxidase activities and that the transport system itself becomes the limiting factor under conditions of high NADH oxidase activities. Under energy-limiting conditions 135-235 molecules of NADH have to be oxidized in order to transport one molecule of amino acid. At all levels of energy supply a competition by the different amino acid transport systems for the available energy could not be observed. These observations indicate that only a fraction of the energy, generated by the respiratory chain, is used for the transport of an amino acid and that the bulk of the energy dissipates via other channels in the membrane vesicles.

Effect of inhibitors on the substrate-dependent quenching of 9-aminoacridine fluorescence in inside-out membrane vesicles of Escherichia coli

The effect of various inhibitors on the substrate-dependent quenching of the fluorescence of 9-aminoacridine was measured in inside-out membrane vesicles of Escherichia coli. The rate of fluorescence quenching in the presence of inhibitors was dependent on the rate of electron transfer through the respiratory chain with NADH, succinate, D-lactate or DL-glycerol 3-phosphate as substrates. Several patterns of response were given by the inhibitors. Inhibitors competitive with substrate, or those acting only on the dehydrogenases, gave a direct relationship between the extent of inhibition of oxidase activity and the rate of quenching. A biphasic relationship was given by 2-heptyl-4-hydroxyquinoline N-oxide and piericidin A which was due to these compounds acting both as inhibitors of the respiratory chain and, at higher concentrations, as uncoupling agents. Uncouplers inhibited fluorescence quenching with minimal inhibition of oxidase activity. The transmembrane pH difference was calculated from the extent of fluorescence quenching and the intravesicular volume. The maximum pH difference of 3.3--3.7 units was generated by each of the substrates tested.

Proton movements coupled to lactate and alanine transport in Escherichia coli: isolation of mutants with altered stoichiometry in alanine transport

The addition of lactate to lightly buffered suspensions of resting cells of Escherichia coli caused an increase in the pH of the extracellular phase as lactate and protons entered the cell together. From the magnitude of the pH change and the non-electrogenic character of lactate uptake, we concluded that the stoichiometry of the process was 1 proton/lactate anion. The addition of alanine caused a slow increase in pH, also apparently due to the transport of the amino acid by a symport mechanism with 1 proton/alanine stoichiometry. When cells were grown in the chemostat with alanine as sole carbon source and as limiting nutrient, this stoichiometry was found to alter to 2 protons/alanine, and then to 4 protons/alanine. These increases stoichiometries were due to the selection of mutants. The consequences of these changes on the potential uptake capacity of the cells are discussed.

Dicarboxylic acid transport in membrane vesicles from Bacillus subtilis

Membrane vesicles isolated from Bacillus subtilis W23 catalyze active transport of the C4 dicarboxylic acids L-malate, fumarate, and succinate under aerobic conditions in the presence of the electron donor reduced beta-nicotinamide adenine dinucleotide or the non-physiological electron donor system ascorbate-phenazine methosulfate. The dicarboxylic acids are accumulated in unmodified form. Inhibitors of the respiratory chain, sulfhydryl reagents, and uncoupling agents inhibit the accumulation of the dicarboxylic acids. The affinity constants for transport of L-malate, fumarate, and succinate are 13.5, 7.5, and 4.3 muM, respectively; these values are severalfold lower than those reported previously for whole cells. Active transport of these dicarboxylic acids occurs via one highly specific transport system as is indicated by the following observations. (i) Each dicarboxylic acid inhibits the transport of the other two dicarboxylic acids competitively. (ii) The affinity constants determined for the inhibitory action are very similar to those determined for the transport process. (iii) Each dicarboxylic acid exchanges rapidly with a previously accumulated dicarboxylic acid. (iv) Other metabolically and structurally related compounds do not inhibit transport of these dicarboxylic acids significantly, except for L-aspartate and L-glutamate. However, transport of these dicarboxylic amino acids is mediated by independent system because membrane vesicles from B. subtilis 60346, lacking functional dicarboxylic amino acid transport activity, accumulate the C4 dicarboxylic acids at even higher rates than vesicles from B. subtilis W 23. (v) A constant ratio exists between the initial rates of transport of L-malate, fumarate, and succinate in all membrane vesicle preparations isolated from cells grown on various media. This high-affinity dicarboxylic acid transport system seems to be present constitutively in B. subtilis W23.

Transport of amino acids in membrane vesicles of Rhodopseudomonas spheroides energized by respiratory and cyclic electron flow

Active transport of amino acids in whole cells and membrane vesicles from the facultative photo-synthetic bacterium Rhodopseduomonas spheroides is coupled to electron flow in the respiratory chain and in the cyclic electron transfer system. In vesicles made from cells grown aerobically in the dark transport of amino acids is most effectively energized by the oxidation of NADH and to a lesser extent by ascorbate or succinate in the presence of N,N,N',N'-tetramethyl-1, 4-phenyldiamine dihydrochloride or by ascorbate + phenazine methosulphate via the respiratory chain with oxygen as terminal electron acceptor. In membrane vesicles from cells grown anaerobically in the light the energy for active transport of amino acids is supplied upon illumination by photo-oxidation of bacteriochlorophyll and subsequent electron flow through the cyclic electron transfer system. The initial rate of transport increases with the light intensity upto saturation levels. In both vesicle preparations, inhibitors of electron transfer flow inhibit amino acid uptake. In order to obtain light-driven amino acid transport the isolation of membrane vesicles needs to be performed in a medium with a redox potential between 0 and 100 mV. Illumination of vesicles made from cells grown anaerobically in the light results in the generation of a membrane potential as is indicated by the uptake of the lipophylic cation triphenyl-methylphosphonium.

Prosthecae of Asticcacaulis biprosthecum: system for the study of membrane transport

Prosthecae removed from cells of Asticcacaulis biprosthecum were examined for their ability to accumulate proline, alanine, aspartate, glutamate, and glucose against a concentration gradient. The transport of all of these compounds into prosthecae was stimulated by the nonphysiological electron donors phenazine methosulfate and N,N,N',N'-tetramethyl-p-phenylene diamine dihydrochloride. Reduced pyridine nucleotides caused very slight stimulation of transport of proline and glucose. Other physiological electron donors did not stimulate uptake. Evidence is presented indicating that the failure of certain potential electron donors to drive respiratory chain-linked transport is due to the inabilityof these compounds to enter prosthecae rather than to the absence of enzymes for their oxidation in prosthecae. Inhibition of respiration and uncouplers of oxidative phosphorylation, with the exception of arsenate, inhibit active transport systems of prosthecae.

Amino acid transport in membrane vesicles of obligately anaerobic Veillonella alcalescens

Membrane vesicles of Veillonella alcalescens, grown in the presence of L-lactate and KNO-3, actively transport amino acids under anaerobic conditions in the presence of several electron donors and the electron acceptor nitrate. The highest initial rates of uptake are obtained with L-lactate, followed by reduced nicotinamide adenine dinucleotide, glycerol-1-phosphate, formate, and L-malate.. The membrane vesicles contain the dehydrogenases for these electron donors, and these enzymes are coupled with nitrate reductase. In membrane vesicles from cells, grown in the presence of nitrate, the dehydrogenases are not coupled with fumarate reducatase, and anaerobic transport of amino acids does not occur with fumarate as electron acceptor. Under aerobic conditions none of the physiological electron donors can energize transport. However, a high rate of uptake is observed with the electron donor system ascorbate-phenazine metho-sulfate. This electron donor system also effectively energizes transport under anaerobicconditions in the presence of the electron acceptor nitrate.

Relation between reduced nicotinamide adenine dinucleotide oxidation and amino acid transport in membrane vesicles from Bacillus subtilis

The rate of reduced nicotinamide adenine dinucleotide (NADH) oxidation by membrane vesicles from Bacillus subtilis W23 increases three- to fourfold during logarithmic growth, reaching maximal levels in early stationary phase. Initial rates of L-proline, L-alanine, and L-glutamate transport energized by NADH closely parallel the increase in NADH oxidation. In vesicles prepared at different stages of growth, a constant number of NADH molecules varying from 150 to 260 have to be oxidized to transport one molecule of amino acid. Membrane vesicles from B. subtilis aroD (strain RB163), a mutant defective in menaquinone synthesis, do not transport amino acids in the presence of NADH. Ascorbate plus phenazine methosulfate, however, energizes amino acid transport equally well as in vesicles of B. subtilis W23. NADH oxidation and NADH-driven amino acid transport can be restored instantaneously by the addition of menadione (vitamin K3).

Orientation of membrane vesicles from Escherichia coli as detected by freeze-cleave electron microscopy

The application of freeze-cleave electron microscopy to whole cells of Escherichia coli revealed that the particles exposed on the resulting two inner membrane faces are asymmetrically distributed. This method can therefore be used to determine the orientation of membrane vesicles from E. coli. Membrane vesicles freshly prepared in potassium phosphate buffer (K(+)-vesicles) by osmotic lysis of spheroplasts consisted almost entirely of right-side-out vesicles. Their size suggested that each cell gives rise to one vesicle. When the membrane vesicles were subjected to one cycle of freezing and thawing, the number of inside-out vesicles rose to about 25%. However, due to the small size of most of the inside-out vesicles, these contribute only 2 to 3% of the total membrane surface area of the preparation. The inside-out vesicles appear to arise from infoldings of the membrane of right-side-out vesicles. They also accumulate within the latter, thus producing multivesicular membrane sacs. Na(+)-vesicles (vesicles prepared in sodium phosphate buffer) subjected to freezing and thawing appeared to lose structural rigidity more than did K(+)-vesicles. In contrast to the membrane vesicles prepared by the osmotic lysis of spheroplasts, those obtained by breaking intact cells by a single passage through a French pressure cell were uniformly very small (only 40 to 110 nm in diameter); approximately 60 to 80% were inside-out. To reconcile the polarity of the membrane vesicles with the enzymic activities of such preparations, we propose that "dislocation" of membrane proteins occurs during osmotic lysis of spheroplasts.