Separation by density gradient centrifugation of two types of membranes from spheroplast membrane of Escherichia coli K12

Porin from bacterial and mitochondrial outer membranes

The outer membrane of gram-negative bacteria acts as a molecular filter with defined exclusion limit for hydrophilic substances. The exclusion limit is dependent on the type of bacteria and has for enteric bacteria like Escherichia coli and Salmonella typhimurium a value between 600 and 800 Daltons, whereas molecules with molecular weights up to 6000 can penetrate the outer membrane of Pseudomonas aeruginosa. The molecular sieving properties result from the presence of a class of major proteins called porins which form trimers of identical subunits in the outer membrane. The porin trimers most likely contain only one large but well-defined pore with a diameter between 1.2 and 2 nm. Mitochondria are presumably descendents of gram-negative bacteria. The outer membrane of mitochondria contains in agreement with this hypothesis large pores which are permeable for hydrophilic substances with molecular weights up to 6000. The mitochondrial porins are processed by the cell and have molecular weights around 30,000 Daltons. There exists some evidence that the pore is controlled by electric fields and metabolic processes.

Location of some proteins involved in peptidoglycan synthesis and cell division in the inner and outer membranes of Escherichia coli

Inner and outer membranes of Escherichia coli were separated by isopycnic centrifugation in sucrose gradients and analyzed for the presence of penicillin-binding proteins. All penicillin-binding proteins--except penicillin-binding protein 3, which is found almost exclusively in the cytoplasmic membrane and is involved in septum formation--are also found in gradient fractions corresponding to the outer membrane. Our results support the hypothesis that approximately half of the total amount of penicillin-binding proteins may be sacculus-located proteins linked to the outer membrane, probably through peptidoglycan bridges.

Isolation and characterization of the outer membrane and lipopolysaccharide from Eikenella corrodens

The chemical composition of the outer membrane fractions (OMFs) of Eikenella corrodens strains 23834 and 470 as well as the strain 23834 lipopolysaccharide (LPS) was determined. The OMFs were obtained by Triton X-100 treatment of the heavier membrane fraction from sucrose density centrifugation of the total membrane fraction. The resulting OMFs of strains 23834 and 470, free of cytoplasmic membrane components, were found to contain 69.6 and 75.0% (wt/wt) protein, 4.8 and 9.2% lipid, 4.6 and 4.7% carbohydrate, and 2.0 and 4.6% muramic acid, respectively. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis both OMFs contained one major peptide determined to be 33,500 daltons for the strain 23834 OMF, and 37,500 daltons for the strain 470 OMF. Analysis of the OMF fatty acids revealed hexadecanoic, hexadecenoic, octadecenoic, and lesser amounts of octadecanoic acids. Transmission electron microscopic examination of the OMFs revealed typical large sheets of membrane. Structures (10 nm in diameter) resembling pores were also evident. The E. corrodens LPS was found to be composed of 34.5% (wt/wt) carbohydrate and 25.0% lipid A. Only minute amounts of 2-keto-3-deoxyoctonate and heptose could be detected. Fatty acid analysis revealed primarily octadecanoic and hexadecanoic acids, with lesser amounts of octadecenoic acid. No hydroxy fatty acids were detected. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed the E. corrodens LPS to resemble other smooth-type LPSs. Transmission electron microscopic examination revealed a vesicle-like morphology. The E. corrodens LPS appears not to be a "classical," i.e., enteric, type of LPS.

Molecular requirements for B-lymphocyte activation by Escherichia coli lipopolysaccharide

Certain Escherichia coli mutants altered in phosphatidylglycerol metabolism accumulate fatty acyl derivatives of glucosamine 1-phosphate. Especially prominent is 2,3-diacylglucosamine 1-phosphate (previously designated lipid X), which may be an early precursor of lipid A. We have examined the activity of lipid X (Mr = 711.9) and several related compounds as mitogens towards mouse lymphocytes. As judged by labeling with [methyl-3H]thymidine, lipid X is mitogenic, and it mimics the properties of lipopolysaccharide and lipid A. The following evidence suggests that lipid X exerts its effects by a route similar to that of lipopolysaccharide: (i) lymphocytes from C3H/HeJ mice, which are unresponsive to lipopolysaccharide, are also not stimulated by lipid X; (ii) polymyxin B abrogates lymphocyte stimulation by lipid X; and (iii) lipid X induces the proliferation and maturation of lymphocytes to antibody-producing plaque-forming cells. Selective removal of the ester-linked hydroxymyristate moiety at position 3 totally abolishes mitogenic activity. Other phospholipids, such as phosphatidic acid, CDP-diglyceride, phosphatidylcholine, and lysophosphatidylcholine, have no activity as mitogens. If lipid X and lipid A induce by common mechanism(s) B-lymphocyte proliferation, then it follows from structural comparison that the reducing-end subunit of lipid A is the minimal structural requirement for this activity. Because the structure of lipid X is completely defined, biochemical and pharmacological dissection of B-cell activation by lipopolysaccharide should now be possible.

Demonstration of a saturable binding site for thyrotropin in Yersinia enterocolitica

Several lines of evidence suggest that there might be immunologic cross-reactivity between the thyroid plasma membrane in humans and antigenic determinants in the enteric pathogen Yersinia enterocolitica. Studies were therefore performed to determine whether Y. enterocolitica, like the thyroid membrane, contains a thyrotropin binding site. A saturable binding site for bovine thyrotropin was indeed demonstrable, particularly in preparations of the organism that have been treated with ethylenediaminetetraacetate and lysozyme. Hormonal specificity of the binding site, as judged from the inhibition of binding of 125I-labeled bovine thyrotropin, was similar to that of the thyrotropin receptor in human thyroid tissue.

Phospholipase A activity in commercial nucleases. Implications for membrane vesicle isolation

Phospholipase A activity was detected in commercial DNAases I and II and in RNAase preparations. The amount of phospholipase correlates inversely with the degree of nuclease purification. The assessment of the level of phospholipase in commercial nucleases is important in cases where enzymatic properties other than those of DNAases and RNAases are to be investigated and when these preparations are to be used in the isolation of biological membranes.

Citrate-tris(hydroxymethyl)aminomethane-mediated release of outer membrane sections from the cell envelope of a deep-rough (heptose-deficient lipopolysaccharide) strain of Escherichia coli O8

A heptose-deficient lipopolysaccharide strain of Escherichia coli O8, strain F515, was found to release portions of its outer membrane when cells were exposed to 10 mM citrate buffer (pH 2.75) for 30 min and subsequently exposed to 100 mM tris(hydroxymethyl)aminomethane buffer (pH 8.00). The outer membrane component release was found to be composed of protein, lipopolysaccharide, phospholipid (cardiolipin, phosphatidylethanolamine, and phosphatidylglycerol), and alkaline phosphatase. The outer membrane component was released from the cell envelope in the absence of cell lysis, as no glucose-6-phosphate dehydrogenase activity or succinic dehydrogenase activity was detected. Morphologically, the outer membrane component appeared to consist of laminar fragments and vesicles which had an associated alkaline phosphatase activity.

Studies on the damage to Escherichia coli cell membrane caused by different rates of freeze-thawing

Freeze-thawing of Escherichia coli cells caused a release of cell membrane components such as protein, phospholipids and lipopolysaccharides. A greater amount of release and a lesser extent of cell survival were seen in slow freeze-thawing than in rapid freeze-thawing. Several dehydrogenases in the cells were also freed. The mode of release was also dependent on the rate of freeze-thawing. The materials released by slow freeze-thawing were found to be mostly composed of outer membrane components, whereas the materials released by rapid freeze-thawing contained cytoplasmic as well as outer membrane components. The chemical composition of these fragments differed significantly from that of the original membranes. The relative content of cytoplasmic membrane-bound enzymes in these fragments also differed from that of the cytoplasmic membrane. The fragmentation was assumed to have resulted mainly from the crystallization of external water. In slow fraeeze-thawing, it was considered that the phase separation of the membrane phospholipid bilayer increased the possibility of outer membrane fragmentation. Rapid freeze-thawing caused cytoplasmic membrane damage to the cells as well as to the outer membrane. In rapid freeze-thawing, the effect of phase separation appeared to be small because of rapid passage through the transition temperatures. The presence of 10% glycerol completely inhibited the release of cellular materials and enzymes. Cell survival was maintained at a high level in the glycerol-treated samples whether freeze-thawed slowly or rapidly.

Characterization of the cell wall and cell wall proteins of Chromatium vinosum

Highly purified cell walls of Chromatium vinosum were isolated by differential centrifugation, with or without Triton X-100 extraction. The isolated material had a protein composition similar to that of cell walls obtained by sucrose density gradient centrifugation. Twenty-two proteins were reproducibly detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A 42-kilodalton protein was shown to account for 65% of the total cell wall protein. The majority of cell wall proteins were solubilized in sodium dodecyl sulfate at room temperature; however, they existed as high-molecular-weight complexes unless heated to 45 degrees C or above. The cell wall contained one heat-modifiable protein which migrated with an apparent molecular weight of 37,400 when solubilized at 70 degrees C or below, but which migrated with an apparent molecular weight of 52,500 if solubilized at 100 degrees C. The electrophoretic mobility of three proteins was modified by 2-mercaptoethanol. The majority of C. vinosum cell wall proteins had isoelectric points between pH 4.5 and 5.5, and the 42-kilodalton protein focused at pH 4.9. No proteins were detected which were analogous to the lipoprotein or peptidoglycan-associated proteins of the Enterobacteriaceae. Nearest-neighbor analysis with a reducible, cross-linking reagent indicated that three proteins, including the 42-kilodalton protein, associated with themselves. Most of the cell wall proteins were partially accessible to proteases in both intact cells and isolated cell walls. Protease treatment of the whole cell or isolated cell wall digested approximately an 11,000-molecular-weight portion of the 42-kilodalton protein.

Interaction of bacteriophage T4 with reconstituted cell envelopes of Escherichia coli K-12

The interaction with bacteriophage T4 of the cell surface of Escherichia coli K-12 reconstituted from outer membrane protein O-8, lipopolysaccharide, and the lipoprotein-bearing peptidoglycan sacculus was studied. The reconstituted cell surface was active as a receptor for the phage, resulting in the contraction of the tail sheath, a morphological change in the base plate which was accompanied by the extension of short tail pins down to the cell surface and the penetration of the needle through the cell surface. However, the ejection of phage deoxyribonucleic acid did not take place. Both O-8 and lipopolysaccharide were essential for the interaction. In the reconstitution, the wild-type lipopolysaccharide could not be replaced by either heptoseless lipopolysaccharide or lipid A. The lipoprotein-bearing peptidoglycan sacculus was also found to be an active component for the phage adsorption. The sacculus most likely functioned as a basal framework on which O-8 and lipopolysaccharide assembled to form a flat sheet which is large enough to interact with individual distal ends of long tail fibers of a single phage particle.

Protein K: a new major outer membrane protein found in encapsulated Escherichia coli

The protein composition of purified outer membranes of 47 Escherichia coli strains was examined by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis. Of 33 encapsulated strains, all contained an outer membrane protein distinguishable from previously reported proteins. The 14 non-encapsulated strains with one exception lacked this protein. Because of its apparent association with encapsulation (K antigen) we have named it K protein. The protein was purified nearly to homogeneity by chromatography in the presence of detergents, and its composition was determined. Its amino acid composition does not differ significantly from that reported for protein I, another E. coli major outer membrane protein. Furthermore, the N-terminal amino acid sequence of protein K indicates that it is related to protein I.

Membranes of Rhodopseudomonas sphaeroides. V. Identification of bacteriochlorophyll alpha-depleted cytoplasmic membrane in phototrophically grown cells

The separation of membrane fragments was investigated in extracts of phototropically grown Rhodopseudomonas sphaeroides to determine if the plasma membrane contains discrete regions. A highly purified fraction of bacteriochlorophyll alpha-deficient membrane fragments was isolated by differential centrifugation, chromatography on Sepharose 2B, reaggregation, and isopycnic sedimentation on sucrose gradients. Significant levels of b- and c-type cytochromes and succinate dehydrogenase were demonstrated in the isolated membrane fragments and their appearance in electron micrographs, their polypeptide profile in dodecyl sulfate-polyacrylamide gel electrophoresis, and overall chemical composition were essentially identical to a similar fraction isolated from aerobically grown cells. Their polypeptide profiles were distinct from those of the intracytoplasmic chromatophore and outer membranes, and on the basis of bacteriochlorophyll content the phototrophic fraction was contaminated with chromatophores by less than 9%. The membrane fragments contained no diaminopimelic acid or glucosamine. It is condluded that the membrane fragments isolated from phototrophically growing Rp. sphaeroides have arisen from photosynthetic pigment-depleted regions of the plasma membrane structurally and functionally differentiated from the intracytoplasmic chromatophore membrane. These regions represent conserved chemotrophic cytoplasmic membrane whose synthesis continues under photoheterotrophic conditions.

Intracellular location of flexirubins in Flexibacter elegans (Cytophagales)

The inner and outer membranes of 2 strains of Gram-negative Flexibacter elegans, Fx e1 and Fx 3/4, could be separated on sucrose density gradients after the cells had been converted into spheroplasts, and the spheroplasts had been lysed in presence of EDTA and the detergent Brij 58. The light fraction (rho = 1.14 g . cm-3) contained the components of the respiratory chain in high concentrations, but only low amounts of the lipopolysaccharide component, 2-keto-3-deoxyoctonic acid, and was thus mainly material from the inner membrane. The heavy fraction (rho = 1.175 g . cm-3) contained only traces of respiratory chain enzymes, but the majority of the 2-keto-3-deoxyoctonic acid, and was thus mainly material from the outer membrane. The flexirubin pigments were found almost quantitatively in the latter fraction. Strain Fx 3/4 produced carotenoids in addition to flexirubins; in this case the flexirubins were located in the outer, and the carotenoids in the inner membrane.

Metal ion dependence of a heat-modifiable protein from the outer membrane of Escherichia coli upon sodium dodecyl sulfate-gel electrophoresis

One heat-modifiable protein of Escherichia coli outer membrane does not completely change to the high-temperature form in the presence of magnesium ion in sodium dodecyl sulfate solution. When the metal ion complexing reagents ethylenediaminetetraacetic acid, phosphate ion, hydroxyl ion, or the competitive cations Zn2+ or Ca2+ are added to the sodium dodecyl sulfate-solubilized sample of outer membrane, and then the sample is heated to 100 degrees C and recooled to room temperature, the protein is almost completely converted to the high-temperature form. In control samples, or if sodium chloride, magnesium chloride, or manganous chloride are added to these samples and treated the same way, a large amount of the low-temperature form of the protein is preserved. beta-Mercaptoethanol additions gave the same results as the metal ion complexing reagents and may owe its activity in these solutions to metal-binding activity and not to its role as a reducing reagent. We concluded that magnesium ion may be involved with stabilization of the low-temperature form of the protein either by directly binding the magnesium or by mediating interaction with other components of the membrane.

Studies on the cell cycle of Myxobacter AL-1. II. Activities of seven enzymes during the cell cycle

The properties of seven enzymes were studied in extracts from Myxobacter AL-1. The enzymes were isocitrate dehydrogenase (E.C.1.1.1.42), succinate dehydrogenase (E.C.1.3.99.1), alkaline phosphatase (E.C.3.1.3.1), alpha-glucosidase (E.C.3.2.1.20), beta-glucosidase (E.C.3.2.1.21), beta-galactosidase (E.C.3.2.1.23), and N-acetyl-glucosaminidase (E.C. 3.2.1.30). Four of these enzymes: isocitrate dehydrogenase, alpha-glucosidase, beta-glucosidase, and beta-galactosidase are cytosolic enzymes. Succinate dehydrogenase was found to be located on the cytoplasmic membrane system, whereas alkaline phosphatase and N-acetylglucosaminidase were considered as enzymes which bind the outer membranes resp. the cell wall. During the cell cycle, all enzymes have a pattern of discontinuous activity increase. Succinate dehydrogenase and isocitrate dehydrogenase exhibit a stepwise increase of activity, whereas the other enzymes follow the pattern of a peak enzyme.

Synthesis and assembly of the membrane proteins in E. coli

Kinetics of integration of membrane proteins were studied in E. coli to discover how membrane proteins find their final location in the functional membrane. The experiments make use of a simple and convenient method developed for isolating inner and outer membranes from a number of small-scale cultures with high recovery. Among the proteins that constitute the cell surface structures, inner membrane proteins are integrated most rapidly after synthesis, whereas outer membrane proteins delay somewhat, and periplasmic proteins delay further in reaching their destinations. Protein I, a major outer membrane protein with molecular weight of about 37,000 daltons, exhibits significantly slower rates of integration than other outer membrane proteins. The decreased fluidity of membrane lipids by temperature shiftdown of an unsaturated fatty acid auxotroph grown on elaidate results in abnormally slow assembly of the outer membrane proteins and also in an anomalous assembly of the inner membrane proteins, suggesting that the fluid state of the lipids is required for normal operation of these processes. The possible relevance of these findings to the mechanism of membrane formation is discussed.

Adenosine 5'-triphosphate-linked transhydrogenase in cytoplasmic membranes of colicin-treated and untreated Escherichia coli

The adenosine 5'-triphosphate (ATP)-linked transhydrogenase reaction, present in the particulate fractions of Escherichia coli, was previously shown to be inhibited in these fractions when the bacteria were treated with colicins K or El. The purpose of this study was to characterized the ATP-linked transhydrogenase reaction and the colicin-caused inhibition of the reaction in purified cytoplasmic membranes. Particulate fractions from bacteria treated or untreated with colicins were separated on sucrose gradients into cell wall membrane and cytoplasmic membrane fractions. The ATP-linked transhydrogenase reaction was found to be exclusively associated with the cytoplasmic membrane fractions. The reaction was inhibited by carbonylcyanide m-chlorophenlhdrazone, dinitrophenol, N,N'-dicyclohexylcarbodiimide, and trypsin. Although the cytoplasmic membrane fractions were purified from the majoriy of the cell wall membrane and its bound colicins, they showed the inhibitory effects of colicins K and El on the ATP-linked transhydrogenase reaction. The inhibition of ATP-linked transhydrogenase reaction induced by the colicin could not be reversed by subjection the isolated membranes to a variety of physical and chemical treatments. Cytoplasmic membranes depleted of energy-transducing adenosine triphosphatase ATPase) complex (coupling factor) lost the ATP-linked transhydrogenase activity. The ATPase complexes isolated from membranes of bacteria treated or untreated with colicins El or K reconstituted high levels of ATP-linded transhydrogenase activity to depleted membranes of untreated bacteria. The same ATPase complexes reconstituted low levels of activity to depleted membranes of the treated bacteria.

Membrane associated components of the bacterial flagellar apparatus

At the position of insertion of the flagellum into the Gram-negative bacterial cell envelope, a specialized membrane differentiation has been observed by electron microscopy. This structure, termed concentric membrane rings, is harboured on the under-side of the outer membrane of Spirillum serpens, and forms a plate-like array of up to seven rings (diameter 90 nm) and an interior supporting collar. The concentric membrane rings are sensitive to proteolytic digestion, but are lysozyme and phospholipase resistant. The structures are disrupted by ionic detergents, yet resistant to the action of non-ionic detergents. A model integrating the basal organelle of the bacterial flagellum and the outer membrane of the cell wall is presented.

Interaction of membrane aminophospholipids of E. coli with fluorodinitrobenzene and trinitrobenzenesulfonate

E. coli cells were reacted with TNBS in bicarbonate-NaCl buffer, pH 8.5 (buffer A) and in phosphate-NaCl buffer, pH 7.0 (buffer B). In buffer A, DNP-GPE is the major product when FDNB is used. DNP-PE and DNP-LPE are formed in lesser amounts. Phospholipase A activity is high in buffer A. When TNBS is used, the labeling of the lipid components is less than with FDNB and more TNP-PE is formed relative to TNP-GPE. This data suggests that the phospholipases which are located primarily on the outer L-membrane of the cell wall act to a lesser extent on TNP-PE than on DNP-PE. E. coli cells were prelabeled with TNBS and FDNB in buffer A, washed and incubated in buffer A. The endogenous labeled DNP-PE gradually decreased with time with a concomitant increase in DNP-LPE and DNP-GPE due to phospholipase A activity. In contrast, the endogenous labeled TNP-PE also decreased with time as did the endogenous labeled TNP-LPE but a new orange lipid was produced. This lipid is believed to be a derivative of TNP-PE in which one of the nitro groups has been reduced to an amino group by nitroreductase. E. coli cells were prelabeled with TNBS and FDNB in buffer A, washed and incubated in buffer B. Under these conditions with both TNBS and FDNB there is an increase in TNP-PE and DNP-PE with a concomitant decrease in TNP-LPE, TNP-GPE, DNP-LPE and DNP-GPE. These results show that at neutral pH acylation occurs to regenerate TNP-PE and DNP-PE. E. coli cells were incubated with exogenous DNP-GPE or TNP-GPE in buffer A. The DNP-GPE and TNP-GPE were rapidly hydrolyzed by a phosphodiesterase to DNP-ethanolamine and TNP-ethanolamine. An orange derivative was formed which was provisionally identified as a derivative of DNP-ethanolamine or TNP-ethanolamine in which a nitro group has been reduced to an amino group by nitroreductase. The phospholipases and acylating enzymes present in the cell wall of E. coli are active on the dinitrophenyl and trinitrophenyl derivatives of PE and LPE and may act in concert to model and repair the plasma membrane.

Distribution of lipopolysaccharide and the detection of a new subfraction in the cell envelope of a marine pseudomonad

The three outer layers of the cell envelope of marine pseudomonad B-16, the loosely bound outer layer, the outer membrane, and the periplasmic space layer, are the only ones containing appreciable amounts of both lipid and carbohydrate. These layers and a fraction released into the medium during growth of the cells were examined for the presence of common antigens by double immunodiffusion using anti-whole serum. Each of the layers, the medium fraction, and lipopolysaccharide (LPS) isolated from the organism were shown to contain two or more diffusible components showing reactions of identity. Thus LPS is found in each of the three outer layers of the cell envelope of this gram-negative bacterium. The periplasmic space layer was found to contain a fraction accounting for 20% of the dry weight of the layer, which was sedimentable at 30,000 x g and contained lipid, protein, and carbohydrate. Double-immunodiffusion tests indicated that the fraction contained at least one of the two antigens present in isolated LPS. A particulate material was released by the cells during growth which gave a positive test for 2-keto-3-deoxyoctulosonic acid and cross-reacted serologically with LPS.

Release of outer membrane fragments from normally growing Escherichia coli

A complex containing lipopolysaccharides, phospholipids and proteine separated from the medium by gelfiltration on Sephadex G-200 or by centrifugation. Electron microscopy revealed that this material is released as vesicles and membrane fragements. To determine the origin of these fragments, they were compared to outer and cytoplasmic membranes with respect to keto-deoxyoctulosonic acid, phospholipid, and protein content, phospholipid composition, fatty acid composition, protein distribution on sodium dodecyl sulfate-polyacrylamide gels, buoyant density, and content of several membrane marker enzymes. The results of this comparison indicate that the membrane fragments found in the culture supernatant of normally growing Escherichia coli consist of practically unmodified outer membrane. Possible mechanisms as to the cause of the release of outer membrane fragments, and its relationship to cell-division, are discussed.

Isolation and characterization of membranes from a hydrocarbon-oxidizing Acinetobacter sp

Membranes were isolated and purified from nutrient broth-yeast extract- and hexadecane-grown cells of Acinetobacter sp. strain HO1-N. Two membrane fractions were isolated from nutrient broth-yeast extract-grown cells, the cytoplasmic membrane and the outer membrane. In addition to these two membrane fractions, a unique membrane fraction was isolated from hexadecane-grown cells (band 1) and characterized as a lipid-rich, low-density membrane containing high concentrations of hexadecane. The outer membrane preparations of Acinetobacter, obtained from nutrient broth-yeast extract- and hexadecane-grown cells, exhibited a low ratio of lipid phosphorus to protein and contained phospholipase activity and 2-keto-3-deoxyoctulosonic acid. Phosphatidic acid cytidyltransferase, adenosine triphosphatase, and reduced nicotinamide adenine dinucleotide oxidase were recovered almost exclusively in the cytoplasmic membrane fractions. The cytoplasmic membrane fractions contained 20 to 25 polypeptide species on sodium dodecyl sulfate-polyacrylamide gels, and the outer membrane fractions contained 15 to 20 polypeptide species. A major polypeptide species with an apparent molecular weight of approximately 42,000 to 44,000 was found for all outer membrane fractions. The buoyant densities of the cytoplasmic membrane fractions and the outer membrane fractions were closely similar, necessitating their separation by differential centrifugation. Band 1 of hexadecane-grown cells had a ratio of lipid phosphorus to protein that was almost twice that of cytoplasmic membrane and a correspondingly low buoyant density (1.086 g/cm3). Enzyme activities associated with band 1 were identical to those associated with the cytoplasmic membrane. The electrophoretic banding pattern of band 1 was essentially identical to the banding pattern of the cytoplasmic membrane. The phospholipid and neutral lipid compositions of the isolated membrane fractions were determined as qualitatively similar, with significant quantitative differences. The ultrastructure characteristics of the respective membrane fractions were examined by the negative-stain technique.

Differential reaction of cell membrane phospholipids and proteins with chemical probes

The major aims of this study were to determine the degree of phospholipid asymmetry and the neighbor analysis of phospholipids in different types of cell membranes. For this study a penetrating probe (FDNB), a non-penetrating probe (TNBS) and a cross-linking probe (DFDNB) were used. The reaction of hemoglobin, membrane protein and membrane PE and PS of erythrocytes with DFNB and TNBS was studied over a concentration range of 0.5 to 10 mM probe. TNBS reacts to an extremely small extend with hemoglobin over the concentration range 0.4 to 4 mM whereas FDNB reacts with hemoglobin to a very large extent (50 fold more than TNBS). The reaction of membrane protein of intact erythrocytes reaches a sharp plateau at 1 mM TNBS whereas the reaction of membrane protein goes to a much larger extent with FDNB with no plateau seen up to 4 mM FDNB. This data shows that TNBS does not significantly penetrate into the cell under our conditions whereas FDNB does penetrate into the cell. The results show that there are four fold more reactive sites on proteins localized on the inner surface of the erythrocyte membrane as compared to the outer surface. TNBS at 0.5 to 2 mM concentration does not label membrane PS and labels membrane PE to a small extent. The reaction of PE with TNBS shows an initial plateau at 2 mM probe and a second slightly higher plateau between 4 to 10 mM probe. TNBS from 0.5-2.0 mM does not react with PS, but between 3 to 10 mM concentration, a very small amount of PS reacts with TNBS. Hence above 2 mM TNBS or FDNB a perturbation occurs in the membrane such that more PE and PS are exposed and react with these probes. These results demonstrate that essentially no PS is localized on the outer surface of the membrane and only 5% of the total membrane PE is localized on the outer surface of the erythrocyte membrane. TNBS and FDNB were reacted with yeast, E. coli, and Acholeplasma cells. With yeast cells, FDNB reacts to a much larger extent with PE than does TNBS, indicating that FDNB penetrates into the cell and labels more PE molecules. With E. coli, but not with erythrocytes or yeast cells, phospholipase A activity was very pronounced at pH 8.5 giving rise to a large amount of DNP-GPE from DNP-PE. A phosphodiesterase was also present which hydrolyized DNP-GPE to DNP-ethanolamine. The multilayered structure of the E. coli cell envelop did not permit a definitive interpretation of the results. It is clear, however, that TNBS and FDNB react to a different extent with PE in this cell. The Acholeplasma membrane had no detectable PE or PS but contains amino acid esters of phosphatidylglycerol. The reaction of these components with TNBS and FDNB indicate that these aminoacyl-PG are localized on both surfaces of the membrane, with 31% being on the outer surface and 69% on the inner surface...

Membranes of Rhodospirillum rubrum: isolation and physicochemical properties of membranes from aerobically grown cells

Highly purified preparations of cytoplasmic and outer membrane were isolated from aerobically grown Rhodospirillum rubrum lysed by sequential treatment with lysozyme, ethylenediaminetetraacetate, and Brij 58. The membranes were resolved and separated from other cellular constitutents by a combination of velocity and isopyknic sedimentation in sucrose density gradients. On the basis of their appearance in electron micrographs and their protein profiles in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, these preparations appear to be quite similar to those obtained from other gram-negative bacteria. The cytoplasmic membrane fraction contained the majority of the total membrane-bound succinic dehydrogenase activity and was 10-fold enriched in b- and c-type cytochrome with respect to the outer membrane. The latter fraction was characterized by a much greater carbohydrate content and the presence of arachidic acid, which is typical of R. rubrum lipopolysaccharide. Their protein fatty acid, and overall chemical compositions suggested that these preparations were freer from cross-contamination than those obtained from R. rubrum with currently available methods.

Separation of inner and outer membranes of Rhodopseudomonas spheroides

The separation of inner and outer membrane of Rhodopseudomonas spheroides has been achieved by means of sucrose density gradient (20%, 40%, 60%, w/w) centrifugation. The upper fraction of the gradient, with a specific density 1.181 (g/cm3), is high in cytochrome and succinate dehydrogenase activities, low in lipopolysaccharides and it is designated the inner membrane fraction. The bottom fraction of the gradient, with a specific density 1.240, is high in lipopolysaccharide and contains neither cytochrome nor succinate dehydrogenase activities. This fraction is the cell wall or outer membrane fraction. The intermediate band on the gradient is an unseparated fraction of inner and outer membrane fragments. This fraction has a specific denisty of 1.211 and represents less than 3% of total crude envelope. Thin sections of the vesicles of the inner membrane fraction and those of outer membrane provide morphological evidence for the identity of the individual membrane fractions. At least 22 protein bands are resolved by employing sodium dodecyl sulfate slab gel electrophoresis. Six bands are present only in the inner membrane and two bands are found exclusively in the outer membrane. Most of the remaining polypeptides are present in greater amounts in the inner membrane relative to the outer membrane fractions.

A novel electrophoretic fractionation of Escherichia coli envelopes

Particulate fractions of Escherichia coli have been submitted to electrophoretic fractionation in a buffer stabilized by sucrose gradient. Inner membrane and outer membrane were readily resolved. A combination of electrophoresis, fractional centrifugation and gel filtration can remove remaining contamination by ribosomes and cytoplasm. The presence of particles containing no phospholipids was detected after differential centrifugation. The nature of this fraction is unknown. The inner membrane exhibited heterogeneity on electrophoresis.

Constitution of the cell envelope of Haemophilus influenzae in relation to competence for genetic transformation

Cell envelopes of Haemophilus influenzae have been prepared by breakage in a French pressure cell followed by differential centrifugation. The envelope fraction may be resolved into an inner-membrane (light) and an outer-membrane (heavy) fraction on density gradients. Envelopes from competent cells possess elevated levels of lipopolysaccharide with a composition different from that of log-phase cell envelopes. Three apparently new polypeptides have been observed in envelopes from competent cells by gel electrophoresis in sodium dodecyl sulfate; additional quantitative alterations in the profiles of membrane polypeptides also company the development of the capacity to transport deoxyribonucleic acid. Most of the polypeptide changes are confined to the outer membrane; one new polypeptide is associated with the inner cytoplasmic membrane of competent cells. Protein synthesis during competence developement is rquired for the change in lipopolysaccharides and in the envelope polypeptides to occur.

Cell envelope of Neisseria gonorrhoeae: outer membrane and peptidoglycan composition of penicillin-sensitive and-resistant strains

The cell envelope of Neisseria gonorrhoeae, colony type 4, was studied. Outer membrane was isolated by lysozyme and ethylenediaminetetraacetic acid treatment of plasmolyzed cells according to Wolf-Watz et al. (1973). The degree of purity of the membrane preparations was checked by electron microscopy. The membrane fraction obtained had a density of 1.25 g/cm(3), was rich in phospholipase A and lysophospholipase, and contained only 10% of the total membrane activity of succinate dehydrogenase and d-lactate dehydrogenase. The outer membrane protein profile after sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed at least six major proteins. The predominating protein showed a molecular weight of 35,000. The lipopolysaccharide component was characterized by gas chromatography. The carbohydrates found were galactose, glucose, and glucosamine. d-Glycero-l-manno-heptose was present in very low amounts. Lipid A contained lauric acid, stearic acid, and beta-hydroxy-myristic acid. About 20% of the fatty acids in the outer membrane was derived from lipid A. The phospholipids were characterized as phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol. There was no evidence for a lipoprotein anchored to the peptidoglycan. The peptidoglycan of N. gonorrhoeae was of the chemotype I. The cell envelope of N. gonorrhoeae was found to be highly permeable to gentian violet. Cell envelopes of one penicillin-resistant and two penicillin-sensitive strains were compared. Only moderate differences in fatty acid composition were found.

The outer membrane of Proteus mirabilis. I. Isolation and characterization of the outer and cytoplasmic membrane fractions

1. The crude envelope preparation obtained by sonication of Proteus mirabilis cells in the presence of lysozyme was separated into outer and cytoplasmic membrane fractions by sucrose density gradient centrifugation. The outer membrane fraction accounted for about two thirds of the dry weight of the envelope preparation. 2. In thin sections, the outer and cytoplasmic membrane fractions were shown to consist of vesicles bounded by a single trilaminar membrane, but those of the outer membrane were considerably smaller and were frequently open, forming C-shaped structures. The cytoplasmic membrane vesicles were cleaved by freeze fracturing to expose fracture faces studded with particles, while the outer membrane fragments resisted cleavage. 3. The outer membrane fraction consisted of protein (similar to 40%), lipopolysaccharide (similar to 36%) and lipid (similar to 18%) and had a density of about 1.22 g/cm3. The cytoplasmic membrane fraction consisted mostly of protein (similar to 56%) and lipid (similar to 38%), had a density of about 1.16 g/cm3, and contained almost all the NADH oxidase, succinate and D-lactate dehydrogenase activities of the crude envelope preparation. 4. Electrophoresis in polyacrylamide gels containing sodium dodecylsulfate revealed over 20 polypeptide bands in the cytoplasmic membrane fraction and only 6-7 in the outer membrane fraction. The outer membrane electrophorogram was dominated by a major band (mol. wt 40 000) which was resolved into two bands when electrophoresed in an acidic gel system. Amino acid analysis revealed a higher content of polar amino acids in the protein moiety of the outer membrane.

Isolation and characterization of two outer membrane preparations from Escherichia coli

A method was developed for releasing specifically a part of outer membrane during spheroplast formation. A highly purified outer membrane (outer membrane I) was obtained from the spheroplast medium by isopycnic sucrose gradient centrifugation. The remaining outer membrane (outer membrane II) and cytoplasmic membrane was also isolated from the spheroplasts by the isopycnic centrifugation. Two outer membrane preparations were different from the cytoplasmic membrane in protein composition, enzyme localization, phospholipid composition, lipopolysaccharide content and electron micrographs. Although outer membranes I and II were almost the same in various respects, they seemed to be different from each other under electron microscope and in cardiolipin content. It is suggested that the outer membrane I and the outer membrane II, at least a part of the outer membrane II, are integrated in a different fashion in the outer-most layer of Escherichia coli cell surface.

Isolation and characterization of the outer membrane of Neisseria gonorrhoeae

The cell envelope of Neisseria gonorrhoeae strain 2686, colonial type 4, was isolated from spheroplasts formed by the action of ethylenediaminetetraacetic acid and lysozyme. Isopycnic centrifugation of osmotically ruptured spheroplasts resolved the cell envelope into two main membrane fractions. Chemical and enzymatic analyses were used to characterize these isolated membranes. Succinic dehydrogenase, reduced nicotinamide adenine dinucleotide oxidase, and d-lactate dehydrogenase were localized in the membrane fraction of buoyant density, rho degrees = 1.141 g/cm(3). Lipopolysaccharide and over half of the cell envelope protein were associated with the membrane that banded in sucrose at rho degrees = 1.219 g/cm(3). These fractions were consequently designated cytoplasmic and outer or L-membrane, respectively. Sodium dodecyl sulfate-polyacrylamide electrophoresis of isolated membranes demonstrated the relative simplicity of the protein spectrum of the outer membrane. The majority of the protein in this membrane could be accounted for by proteins of molecular weights 34,500, 22,000, and 11,500. The protein of molecular weight 34,500 accounted for 66% of the total protein of the L-membrane. Isoelectric precipitation at pH 4.6 with 10% acetic acid selectively removed this protein from a 150 mM NaCl in 10 mM tris(hydroxymethyl)aminomethane-hydrochloride, pH 7.4, extract of purified outer membrane. At pH 4.0, the other proteins of the L-membrane were precipitated. It was concluded that the membrane components of the cell envelope of N. gonorrhoeae were similar to those of other gram-negative bacteria. The cell envelope fractions described here, in particular the outer membrane, are sufficiently well defined to provide a valuable tool for future biochemical and immunological studies on N. gonorrhoeae.

Deoxyribonucleic acid-envelope complexes isolated from Escherichia coli by free-flow electrophoresis: biochemical and electron microscope characterization

A procedure for the preparative isolation of Escherichia coli cell wall, membrane, and deoxyribonucleic acid (DNA)-envelope complex fragments has been developed. The envelope fragments were produced by controlled mechanical cell breakage and isolated by density gradient centrifugation and subsequent preparative free-flow electrophoresis. The DNA-envelope complex fragments were shown to contain biochemical markers of both the cell wall and the membrane and by electron microscopy to be cell envelope fragments containing wall/membrane adhesion zones.