Structure and energy-linked activities in reconstituted bacteriorhodopsin--yeast ATPase proteoliposomes.

Bacteriorhodopsin-F₁·F₀ (mitochondrial oligomycin-sensitive ATPase complex) proteoliposomes have poor proton pumping and photophosphorylation activities when reconstituted by cholate dialysis. A considerable proportion of the bacteriorhodopsin is not incorporated by cholate dialysis, the particles being too large to be combined into liposomes. Much better reconstitution is achieved where the purple membranes are first fragmented by sonication. Optimal incorporation occurs where bacteriorhodopsin and the phospholipids are sonicated together, suggesting that some perturbation of the liposomes is necessary for successful integration. Since F₁·F₀ is denatured by sonication a two-step reconstitution procedure has been developed wherein bacteriorhodopsin is first incorporated by sonication, then F₁·F₀ by cholate dialysis. The vesicles have high phosphorylation rates and also catalyze postillumination [³²P]ATP formation where pyridine is present during first stage illumination.F₁·F₀ can also be incorporated into sonicated bacteriorhodopsin vesicles by “direct incorporation.” This depends on the presence of negatively charged amphiphiles such as cholate or phosphatidylserine in the membranes, and is stimulated by divalent metal cations. Optimum conditions for the various reconstitution procedures are described.     

Formation of ATP by the adenosine triphosphatase complex from spinach chloroplasts reconstituted together with bacteriorhodopsin

The energy-linked ATPase complex has been isolated from spinach chloroplasts. This protein complex contained all the subunits of the chloroplast coupling factor (CF₁) as well as several hydrophobic components. When the activated complex was reconstituted with added soybean phospholipids, it catalyzed the exchange of radioactive inorganic phosphate with ATP. Sonication of the complex into proteoliposomes together with bacteriorhodopsin yielded vesicles that catalyzed light-dependent ATP formation. Both the ³²P_i-ATP exchange reactions and ATP formation were sensitive to uncouplers such as 3-tert-butyl-5,2′-dichloro-4′-nitrosalicylanilide, bis-(hexafluoroacetonyl)acetone and carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone, that act to dissipate a proton gradient. The energy transfer inhibitors dicyclohexylcarbodiimide, triphenyltin chloride and 2-β-d-glucopyranosyl-4,6′-dihydroxydihydrochalcone were also effective inhibitors of both reactions.     

Energy-linked activities in reconstituted yeast adenosine triphosphatase proteoliposome. Adenosine triphosphate formation coupled with electron flow between ascorbate and ferricyanide.

(1) Conditions are described wherein the yeast oligomycin-sensitive adenosine triphosphatase (ATPase) complex can be reconstituted together with phospholipids to yield extremely high rates of ATP-³²P_j exchange. The vesicles so formed exhibit proton uptake upon addition of Mg²⁺-ATP and a relatively slow decay of the proton gradient. (2) The stimulation of ATP-³²P_i exchange by valinomycin + K⁺ reported previously (Ryrie, I. J. (1975) Arch. Biochem. Biophys. 168, 704–711) is apparently not simply due to a diffusion potential. The findings suggest that an electroimpelled, valinomycin-dependent migration of K⁺ may occur together with the electrogenic movements of protons during ATP hydrolysis and synthesis to establish optimal energized conditions for ATP-³²P_i exchange. (3) An artificial oxidative phosphorylation system in the reconstituted vesicles is described: [³²P]ATP formation from ADP and ³²P_i is shown to be linked with electron flow between external ascorbate and internal ferricyanide where a permeable proton carrier, such as phenazine methosulfate, is used to establish a proton gradient. That the yeast ATPase is capable of net ATP synthesis has also been demonstrated in a light-dependent reaction using ATPase proteoliposomes reconstituted together with bacteriorhodopsin.     

ATP synthesis catalyzed by purified DCCD-sensitive ATPase incorporated into reconstituted purple membrane vesicles

Purified dicyclohexylcarbodiimide-sensitive ATPase from a thermophilic bacterium (TF₀·F₁) and purple membranes from Halobacterium halobium were incorporated into P-lipid vesicles. The reconstituted vesicles took up protons dependent on either illumination or addition of ATP. Net formation of ATP was observed when the vesicles were illuminated in the presence of ADP and Pi and this was completely abolished by addition of an uncoupler or energy transfer inhibitor. These results indicate that purified DCCD-sensitive ATPase, consisting of 8 kinds of polypeptides, was capable of ATP synthesis coupled with proton translocation.     

Purification and reconstitution of the 32Pi-ATP exchange activity of bovine chromaffin granule membrane

Ghosts derived from bovine chromaffin granules have a ³²P_i-ATP exchange activity which is associated with the H⁺ pump of that membrane. This activity was low when compared to bacteria, chloroplasts or submitochondrial particles, but had similar properties (K_m for ATP and P_i, ATP/Mg²⁺ ratio, pH profile, inhibition by dicyclohexylcarbodiimide and tributyltin) to the ATPase from above membranes. The ³²P_i-ATP exchange activity was solubilized by cholate/octylglucoside mixtures. The soluble extract was lipid depleted by ammonium sulfate fractionation and partially purified by sucrose gradient centrifugation. The purified preparation was reconstituted with phospholipids by freeze-thawing. The reconstituted vesicles had a ³²P_i-ATP exchange sensitive to dicyclohexylcarbodiimide and trybutyltin and an ATPase with a sensitivity to the inhibitors which varied with the reconstitution conditions. The α- and β-subunits of F₁-ATPase were major components of the preparation.     

Reconstitution of an ATP-dependent sodium pump with an ATPase from electric eel and pure phospholipids.

An ATP-dependent sodium pump was reconstituted with an ATPase preparation from the electric eel and purified phospholipids. Vesicles reconstituted by the sonication procedure catalyzed Na⁺ translocation at a rate 10 to 20 times higher than vesicles reconstituted by the cholate-dialysis procedure. A small but reproducible stimulation of Na⁺ transport by valinomycin in the presence of K⁺ was observed.     

F0F1 ATP synthase of Streptomycetes: Modulation of activity and oligomycin resistance by protein Ser/Thr kinases

Inverted membrane vesicles of Gram-positive actinobacteria Streptomyces fradiae, S. lividans, and S. avermitilis have been prepared and membrane-bound F₀F₁ ATP synthase has been biochemically characterized. It has been shown that the ATPase activity of membrane-bound F₀F₁ complex is Mg²⁺-dependent and moderately stimulated by high concentrations of Ca²⁺ ions (10–20 mM). The ATPase activity is inhibited by N,N′-dicyclohexylcarbodiimide and oligomycin A, typical F₀F₁ ATPase inhibitors that react with the membrane-bound F₀ complex. The assay of biochemical properties of the F₀F₁ ATPases of Streptomycetes in all cases showed the presence of ATPase populations highly susceptible and insensitive to oligomycin A. The in vitro labeling and inhibitory assay showed that the inverted phospholipid vesicles of S. fradiae contained active membrane-bound Ser/Thr protein kinase(s) phosphorylating the proteins of the F₀F₁ complex. Inhibition of phosphorylation leads to decrease of the ATPase activity and increase of its susceptibility to oligomycin. The in vivo assay confirmed the enhancement of actinobacteria cell sensitivity to oligomycin after inhibition of endogenous phosphorylation. The sequencing of the S. fradiae genes encoding oligomycin-binding A and C subunits of F₀F₁ ATP synthase revealed their close phylogenetic relation to the genes of S. lividans and S. avermitilis.     

Solubilization of a functionally active proline carrier from membranes of Escherichia coli with an organic solvent.

A proline transport carrier was extracted from the membranes of Escherichia coli with acidic n-butanol. Vesicles reconstituted from the butanol extract and E. coli phospholipids and preloaded with K⁺ showed rapid uphill uptake of proline when energy was supplied as a membrane potential introduced by K⁺-diffusion via valinomycin. Proline uptake by the reconstituted vesicles, like that of intact cells and isolated membrane vesicles, was inhibited by 3,4-dehydroproline, SH reagents, and a proton conducting uncoupler. Reconstituted vesicles of mutants defective in proline transport showed little or no proline uptake. The proline carrier was partially purified from the extract and separated from the bulk of phospholipids on Sephadex LH-20.     

The yeast mitochondrial adenosine triphosphatase complex. Purification, subunit composition, and some effects of protease inhibitors.

(i) The method of preparing the oligomycin-insensitive F₁-ATPase by chloroform treatment of mitochondrial membranes (Beechey et al., 1975, Biochem. J.148, 533–537) has been modified such that a five-subunit protein is obtained from yeast with an activity of 140 μmol of ATP hydrolyzed/min/mg of protein. Repetition of this procedure in the presence of protease inhibitors (in particular, p-aminobenzamidine) allows isolation of a four-subunit protein with an activity of 243 μmol of ATP hydrolyzed/min/ mg of protein, (ii) A modified procedure is described for the preparation of the yeast oligomycin-sensitive F₁-F₀ ATPase complex, making use of protease inhibitors throughout and solubilization of the ATPase from mitochondrial membranes using Triton X-100 and sodium deoxycholate simultaneously. Two polypeptides Of 42,000 and 29,000 molecular weight are eliminated, the largest corresponding to the missing band of the F₁ sector. The complex retains oligomycin- and uncoupler-sensitive ATP-³²P_i exchange and ATP-driven proton uptake, indicating the retention of a complete coupling mechanism. (iii) F₁-ATPase is released from the F₁-F₀ complex by brief heating at 50 °C in the presence of ATP. The remaining hydrophobic polypeptides aggregate and are isolated by centrifugation. The F₁ sector can be isolated containing either four or five subunits depending on whether the starting F₁-F₀ complex contained the 42,000 and 29,000 molecular weight polypeptides. (iv) Sensitivity of the F₁-F₀ ATPase complex to oligomycin and dicyclohexylcarbodiimide varies considerably depending on the activity measured and whether the complex was first reconstituted with phospholipids. The degree of inhibitor sensitivity is considered a poor guide to intactness of the complex.     

Proton Transport Activity of the Purified Vacuolar H-ATPase from Oats : Direct Stimulation by Cl

To determine whether the detergent-solubilized and purified vacuolar H⁺-ATPase from plants was active in H⁺ transport, we reconstituted the purified vacuolar ATPase from oat roots (Avena sativa var Lang). Triton-solubilized ATPase activity was purified by gel filtration and ion exchange chromatography. Incorporation of the vacuolar ATPase into liposomes formed from Escherichia coli phospholipids was accomplished by removing Triton X-100 with SM-2 Bio-beads. ATP hydrolysis activity of the reconstituted ATPase was stimulated twofold by gramicidin, suggesting that the enzyme was incorporated into sealed proteoliposomes. Acidification of K⁺-loaded proteoliposomes, monitored by the quenching of acridine orange fluorescence, was stimulated by valinomycin. Because the presence of K⁺ and valinomycin dissipates a transmembrane electrical potential, the results indicate that ATP-dependent H⁺ pumping was electrogenic. Both H⁺ pumping and ATP hydrolysis activity of reconstituted preparations were completely inhibited by <50 nanomolar bafilomycin A₁, a specific vacuolar type ATPase inhibitor. The reconstituted H⁺ pump was also inhibited by N,N′-dicyclohexylcarbodiimide or NO₃⁻ but not by azide or vanadate. Chloride stimulated both ATP hydrolysis by the purified ATPase and H⁺ pumping by the reconstituted ATPase in the presence of K⁺ and valinomycin. Hence, our results support the idea that the vacuolar H⁺-pumping ATPase from oat, unlike some animal vacuolar ATPases, could be regulated directly by cytoplasmic Cl⁻ concentration. The purified and reconstituted H⁺-ATPase was composed of 10 polypeptides of 70, 60, 44, 42, 36, 32, 29, 16, 13, and 12 kilodaltons. These results demonstrate conclusively that the purified vacuolar ATPase is a functional electrogenic H⁺ pump and that a set of 10 polypeptides is sufficient for coupled ATP hydrolysis and H⁺ translocation.     

Purification and functional properties of the DCCD-reactive proteolipid subunit of the H+-translocating ATPase from Mycobacterium phlei

Interaction of N,N′-dicyclohexylcarbodiimide (DCCD) with ATPase of Mycobacterium phlei membranes results in inactivation of ATPase activity. The rate of inactivation of ATPase was pseudo-first order for the initial 30–65% inactivation over a concentration range of 5–50 μM DCCD. The second-order rate constant of the DCCD-ATPase interaction was k = 8.5·10⁵ M^?1·min^?1. The correlation between the initial binding of [¹⁴C]DCCD and 100% inactivation of ATPase activity shows 1.57 nmol DCCD bound per mg membrane protein. The proteolipid subunit of the F₀F₁-ATPase complex in membranes of M. phlei with which DCCD covalently reacts to inhibit ATPase was isolated by labeling with [¹⁴C]DCCD. The proteolipid was purified from the membrane in free and DCCD-modified form by extraction with chloroform/methanol and subsequent chromatography on Sephadex LH-20. The polypeptide was homogeneous on SDS-acrylamide gel electrophoresis and has an apparent molecular weight of 8000. The purified proteolipid contains phosphatidylinositol (67%), phosphatidylethanolamine (18%) and cardiolipin (8%). Amino acid analysis indicates that glycine, alanine and leucine were present in elevated amounts, resulting in a polarity of 27%. Cysteine and tryptophan were lacking. Butanol-extracted proteolipid mediated the translocation of protons across the bilayer, in K⁺-loaded reconstituted liposomes, in response to a membrane potential difference induced by valinomycin. The proton translocation was inhibited by DCCD, as measured by the quenching of fluorescence of 9-aminoacridine. Studies show that vanadate inhibits the proton gradient driven by ATP hydrolysis in membrane vesicles of M. phlei by interacting with the proteolipid subunit sector of the F₀F₁-ATPase complex.     

Solubilization,purification and reconstitution of Ca-ATPase from bovine pulmonary artery smooth muscle microsomes by different detergents: Preservation of native structure and function of the enzyme by DHPC

The properties of Ca²⁺-ATPase purified and reconstituted from bovine pulmonary artery smooth muscle microsomes {enriched with endoplasmic reticulum (ER)} were studied using the detergents 1,2-diheptanoyl-sn-phosphatidylcholine (DHPC), poly(oxy-ethylene)8-lauryl ether (C₁₂E₈) and Triton X-100 as the solubilizing agents. Solubilization with DHPC consistently gave higher yields of purified Ca²⁺-ATPase with a greater specific activity than solubilization with C₁₂E₈ or Triton X-100. DHPC was determined to be superior to C₁₂E₈; while that the C₁₂E₈ was determined to be better than Triton X-100 in active enzyme yields and specific activity. DHPC solubilized and purified Ca²⁺-ATPase retained the E1Ca−E1*Ca conformational transition as that observed for native microsomes; whereas the C₁₂E₈ and Triton X-100 solubilized preparations did not fully retain this transition. The coupling of Ca²⁺ transported to ATP hydrolyzed in the DHPC purified enzyme reconstituted in liposomes was similar to that of the native micosomes, whereas that the coupling was much lower for the C₁₂E₈ and Triton X-100 purified enzyme reconstituted in liposomes. The specific activity of Ca²⁺-ATPase reconstituted into dioleoyl-phosphatidylcholine (DOPC) vesicles with DHPC was 2.5-fold and 3-fold greater than that achieved with C₁₂E₈ and Triton X-100, respectively. Addition of the protonophore, FCCP caused a marked increase in Ca²⁺ uptake in the reconstituted proteoliposomes compared with the untreated liposomes. Circular dichroism analysis of the three detergents solubilized and purified enzyme preparations showed that the increased negative ellipticity at 223 nm is well correlated with decreased specific activity. It, therefore, appears that the DHPC purified Ca²⁺-ATPase retained more organized and native secondary conformation compared to C₁₂E₈ and Triton X-100 solubilized and purified preparations. The size distribution of the reconstituted liposomes measured by quasi-elastic light scattering indicated that DHPC preparation has nearly similar size to that of the native microsomal vesicles whereas C₁₂E₈ and Triton X-100 preparations have to some extent smaller size. These studies suggest that the Ca²⁺-ATPase solubilized, purified and reconstituted with DHPC is superior to that obtained with C₁₂E₈ and Triton X-100 in many ways, which is suitable for detailed studies on the mechanism of ion transport and the role of protein–lipid interactions in the function of the membrane-bound enzyme.     

Resolution and Reconstitution of H+-ATPase Complex from Beef Heart Mitochondria

Mitochondrial H⁺-ATPase complex, purified by the lysolecithin extraction procedure, has been resolved into a “membrane” (NaBr-F₀) and a “soluble” fraction by treatment with 3.5 M sodium bromide. The NaBr-F₀ fraction is completely devoid of p, 8, and e subunits of the F, ATPase and largely devoid of α and γ subunits of F₁, where F₀ is used to denote the membrane fraction and F₁, coupling factor 1. This is confirmed by complete loss of ATPase and P₁-ATP exchange activities. The addition of F₁ (400 μg · mg^?1 F₀) results in complete restoration of oligomycin sensitivity without any reduction in the F₁-ATPase activity. Presumably, this is due to release of ATPase inhibitor protein from the F₁-F₀ complex consequent to sodium bromide extraction. Restoration of Pf-ATP exchange and H⁺-pumping activities require coupling factor B in addition to FpATPase. The oligomycin-sensitive ATPase and 32P₁ATP exchange activities in reconstituted Fr F₀ have the same sensitivity to uncouplers and energy transfer inhibitors as in starting submitochondrial particles from the heavy layer of mitochondria and F₁-F₀ complex. The data suggest that the altered properties of NaBr-F₀ observed in other laboratories are probably inherent to their F₁F₀ preparations rather than to sodium bromide treatment itself.

The H⁺-ATPase (F₁-F₀) complex of all known prokaryotic (3, 8, 9, 10, 21, 32, 34) and eukaryotic (11, 26, 30, 33, 35–37) phosphorylating membranes contain two functionally and structurally distinct entities. The hydrophilic component F₁, composed of five unlike subunits, shows ATPase activity that is cold labile as well as uncoupler-and oligomycin-insensitive. The membrane-bound hydrophobic component F₀, having no energy-linked catalytic activity of its own, is indirectly assayed by its ability to regain oligomycin sensitive ATPase and P₁-ATP exchange activities on binding to F¹-ATPase (33). The purest preparations of bovine heart mitochondrial F₀ show seven or eight major components in polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate or SDS-PAGE (1, 2, 12, 14), ranging from 6 to 54 ku in molecular weight (12). The precise structure and polypeptide composition of mitochondrial Fo is not known.

The F₀ preparations from bovine heart reported so far have been derived from H⁺-ATPase preparations isolated in the presence of cholate and deoxycholate (11, 33, 36, 37). The ATPase and P₁-ATP exchange activity of the preparations so obtained are low, dependent upon additional phospholipids and coupling factors; they show altered sensitivity to energy transfer inhibitors as compared to submitochondrial particles from the heavy layer of the mitochondria or ETPh (1. 2, 12, 14, 29, 33). Recently, lysolecithin has been successfully employed to extract highly active H⁺-ATPase from beef (17, 19, 28) and pig (24) heart mitochondria. The beef heart H⁺-ATPase preparation has the same ratio of ATPase to PrATP exchange activity and apparently the same sensitivity to energy transfer inhibitors as submitochondrial particles (17). The present communication describes resolution of this F₁-F₀ preparation using sodium bromide (NaBr) and reconstitution of ATPase and Pr ATP exchange activities. The NaBr-F₀ prepared from this preparation shows no dependence on lipids, and the same or increased sensitivity to energy transfer inhibitors when reconstituted with F₁-ATPase. Furthermore, F₁ ATPase activity does not decrease on binding of F₁ to NaBr-F₀, even though the reconstituted ATPase activity is 99% sensitive to oligomy-cin and dicyclohexylcarbodiimide. These properties are in contrast to the properties of F₀ reported by other workers (12, 14).     

Isolation,characterization, and reconstitution of a solubilized fraction containing the hydrophobic sector of the mitochondrial proton pump

The hydrophobic sector of the mitochondrial ATPase complex was purified by sequential extraction with cholate and octylglucoside, by further differential solubilization with guanidine and cholate in the presence of phosphatidylcholine, and by fractionation with ammonium sulfate. A polypeptide with a mass of 28,000 dalton was present in the purified hydrophobic section which was cleaved by trypsin, resulting in loss of reconstitution activity. In contrast, dicyclohexylcarbodiimide-binding proteolipid remained unimpaired after exposure to trypsin. The³²P_i-ATP exchange activity of the reconstituted ATPase complex was inhibited byp-hydroxymercuribenzoate, which reacted primarily with the 28,000-dalton protein, as monitored by acrylamide gel electrophoresis with¹⁴C-labeled inhibitor. The function of a 22,000-dalton polypeptide and of some minor components in the region of the proteolipid remains unknown. An examination of the phospholipid requirements for reconstitution of an active complex revealed an unexpected discrepancy. With an excess of phosphatidylethanolamine, optimal reconstitution of³²P_i-ATP exchange and ATP synthesis in the presence of bacteriorhodopsin and light was achieved; at a high phosphatidylcholine:phosphatidylethanolamine ratio, the rate of ATP synthesis remained high, but the rate of³²P_i-ATP exchange dropped precipitously. A new procedure is described for the reconstitution of the ATPase complex with purified phospholipids which is stable for at least 15 days.Abbreviations DCCD N,N-dicyclohexylcarbodiimide - STE-DTT buffer sucrose (250 mM), Tricine-KOH (50 mM), EDTA (5 mM), DTT (5 mM), pH 8.0 - F _o a membranous preparation from mitochondria conferring oligomycin (or rutamycin) sensitivity to F₁ - F₁F₆ coupling factors 1 (ATPase) and 6 - OSCP oligomycin-sensitivity-conferring protein - BSA bovine serum albumin - SDS sodium dodecyl sulfate - DTT dithiothreitol - STE buffer sucrose (250 mM), Tricine-KOH (50 mM), EDTA (5 mM) - TUA particles submitochondrial particles prepared by stepwise exposure of light-layer submitochondrial particles to trypsin and urea, then sonic oscillation in the presence of dilute ammonia (pH 10.4) - OG-cholate buffer glycerol (20%), Tricine (50 mM), MgSO₄ (5 mM), DTT (5mM), cholate (0.5%), octylglucoside (0.5%), pH 8.0 - p-HMB p-hydroxymercuribenzoate     

Studies on the immunological properties of complex V (mitochondrial ATP synthetase complex)

Antibody raised in rabbits against Complex V (miochondrial ATP synthetase complex) purified from beef heart mitochondria cross-reacted with Complex V and submitochondrial particles from beef heart, beef adrenals, and rat liver as shown by double-diffusion and rocket immunoelectrophoresis analysis. Of the various isolated and purified components of Complex V, only the oligomycin sensitivity-conferring protein showed strong reactivity with the anti-Complex V antibody, soluble F₁-ATPase reacted very faintly, while F₆ and ATPase inhibitor protein showed no precipitin lines. Crossed immunoelectrophoresis indicated that antigenic determinants recognized by the antibody were present on OSCP and possibly on the dicyclohexylcarbodiimide-binding protein. The components of Complex V could be precipitated from beef heart submitochondrial particles dissolved in Triton X-100 and pretreated with control IgG. When the composition of the immunoprecipitate was compared to that of purified Complex V, all the constituent polypeptides of the latter were present in the immunoprecipitate, except for one polypeptide in the low-molecular-weight region. Incubation of Complex V or submitochondrial particles with the anti-Complex V antibody in the absence of Triton X-100 caused inhibition of ATP-P_i exchange but not of ATPase activity. In the presence of Triton X-100, oligomycin sensitivity of Complex V was lost and the antibody was able to inhibit also the ATPase activity. The enzymic activity of soluble F₁-ATPase was unaffected by the antibody in the absence or presence of Triton X-100. These results suggest that the anti-Complex V antibody might be a useful tool for identifying and probing the role of Complex V components involved in energy transduction.     

Identification of the protein producing transmembrane diffusion pores in the outer membrane of Pseudomonas aeruginosa PA01

The outer membrane of Pseudomonas aeruginosa PA01 is permeable to saccharides of molecular weights lower than about 6000. Triton X-100/EDTA-soluble outer membrane proteins were fractionated by ion-exchange chromatography in the presence of Triton X-100 and EDTA, and the protein contents of the various fractions analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Each of the major protein bands present in the Triton X-100/EDTA soluble outer membrane was separated from one another. Adjacent fractions were pooled, concentrated and extensively dialyzed to reduce the Triton X-100 concentration. Vesicles were reconstituted from lipopolysaccharide, phospholipids and each of these dialyzed fractions, and examined for their ability to retain [¹⁴C]sucrose. Control experiments indicated that the residual levels of Triton X-100 remaining in the dialyzed fractions had no effect on the formation or permeability to saccharides of the reconstituted vesicles. It was concluded that a major outer membrane polypeptide with an apparent weight of 35 000 is a porin, responsible for the size-dependent permeability of the outer membrane.     

Potassium Stimulation of Corn Root Plasmalemma ATPase : II. H-Pumping in Native and Reconstituted Vesicles with Purified ATPase

The stimulation by K⁺ of the initial rate of H⁺-pumping by ATPase was studied in native plasmalemma (Zea mays L. var Mona) vesicles and in reconstituted vesicles with enzyme purified on a glycerol gradient. In reconstituted vesicles, a very high H⁺-pumping rate (200,000% quenching per minute per milligram protein) was obtained with 9-amino-6-chloro-2-methoxyacridine provided that the pump was short-circuited by K⁺-valinomycin. A constant ionic strength was used to prevent indirect stimulation by the electrostatic effects of K⁺ salts. Indirect stimulation of H⁺-pumping by the short-circuiting effect of internal K⁺, could be abolished by using the permeant anions NO₃⁻ and Br⁻ in native, but not in reconstituted vesicles. In both materials, half-stimulation of the H⁺-pumping by K⁺ was observed at about 5 millimolar. The same stimulation was obtained when K⁺ was present only in the external solution or when it was present both outside and inside the vesicles. It was concluded that the stimulating effect of K⁺ on the H⁺-pumping evidenced in these experiments on both native and reconstituted vesicles was due to a direct effect of the cation on the cytoplasmic face of the ATPase. These results are discussed within the context of the hypothesis of an active K⁺ transport driven by the ATPase through a direct H⁺/K⁺ exchange mechanism.     

Resolution and Reconstitution of a Mammalian Membrane

The problem of the resolution and reconstitution of the inner mitochondrial membrane has been approached at three levels. (1) Starting with phosphorylating submitochondrial particles, a "resolution from without" can be achieved by stripping of surface components. The most extensive resolution was recently obtained with the aid of silicotungstate. Such particles require for oxidative phosphorylation the addition of several coupling factors as well as succinate dehydrogenase. (2) Starting with submitochondrial particles that have been degraded by trypsin and urea a resolution of the inner membrane proper containing an ATPase has been achieved. These experiments show that at least five components are required for the reconstitution of an oligomycin-sensitive ATPase: a particulate component, F ₁, Mg⁺⁺, phospholipids, and F_c. Morphologically, the reconstituted ATPase preparations resemble submitochondrial particles. (3) Starting with intact mitochondria individual components of the oxidation chain have been separated from each other. The following components were required for the reconstitution of succinoxidase: succinate dehydrogenase, cytochrome b\, cytochrome c ₁, cytochrome c, cytochrome oxidase, phospholipids and Q ₁₀. The reconstituted complex had properties similar to those of phosphorylating submitochondrial particles; i.e., the oxidation of succinate by molecular oxygen was highly sensitive to antimycin.     

Active Ca2+ transport by vesicles reconstituted from triton X-100-solubilized pigeon erythrocyte membrane

Pigeon erythrocyte membrane was solubilized partially, but relatively unselectively by Triton X-100. Vesicles were reconstituted from mixtures of Triton-solubilized membrane and lipid (phosphatidylcholine plus phosphatidylethanolamine plus cholesterol) by addition of bovine high-density lipoprotein. This efficiently removed the Triton X-100. Sodium dodecyl sulfate-polyacrylamide gel electropherograms of reconstituted vesicles showed band patterns resembling those of the original membrane. The reconstituted vesicles showed ATP-dependent active accumulation of ⁴⁵Ca²⁺. ATP-dependent ⁴⁵Ca²⁺ uptake by the reconstituted vesicles resembled the corresponding activity of the original membrane vesicles; in both preparations the Ca²⁺ uptake rate depended on the square of the Ca²⁺ concentration and had similar $\text{[Ca}{}^{\mathrm{2+}}\text{]}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ values, 0.16 μM and 0.18 μM, respectively.     

Formations of electrochemical proton gradient and adenosine triphosphate in proteoliposomes containing purified adenosine triphosphatase and bacteriorhodopsin.

Proteoliposome vesicles containing both bacteriorhodopsin of Halobacterium halobium and H+-translocating ATPase [EC 3.6,1.3] of a thermophilic bacterium, PS3, (TF0-F1) were reconstituted by either the dialysis method or the sonication method. Generation of the electrochemical proton gradient (deltamuH+) in these vesicles was measured using 9-aminoacridine for estimation of the chemical (deltapH) component and 8-anilinonaphthalene sulfonate for the electrical (deltaphi) component). In illuminated bacteriorhodopsin-vesicles the deltamuH+ reached 180-190 mV when reconstituted by the dialysis method and 210-220 mV when reconstituted by the sonication method. Vesicles reconstituted from both TF0-F1 and bacteriorhodopsin by the dialysis method generated a deltapH+ of about 200 mV on addition of ATP, while vesicles prepared by the sonication method generated very little deltamuH+, if any. These vesicles generated similar deltamuH+ on illumination to that found in bacteriorhodopsin-vesicles. Using vesicles reconstituted from both TF0-F1 and bacteriorhodopsin by the dialysis method, light dependent ATP synthesis was measured in relation to deltamuH+ formation. It was necessary to generate a deltamuH+ of above 170 mV for demonstration of appreciable formation of ATP and the greater the deltamuH+, the faster the rate of ATP synthesis.