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At least 613 records · Page 34Linked to original sources
PubMed1984

The static head method for determining the charge stoichiometry of coupled transport systems. Applications to the sodium-coupled D-glucose transporters of the renal proximal tubule.

The static head method for determining the charge stoichiometry (the number of moles of charge translocated per mole of substrate) of a coupled transport system is presented. The method involves establishing experimental conditions under which a membrane potential exactly balances the thermodynamic driving force of a known substrate gradient. The charge stoichiometry can then be calculated from thermodynamic principles. In contrast to the usual steady-state method for determining charge stoichiometry in cell suspensions and vesicle preparations, the static head method is applicable to systems which are not capable of maintaining a constant membrane potential over time. The charge stoichiometries of two renal sodium coupled D-glucose transporters previously identified in brush-border membrane vesicle preparations from the outer cortex (early proximal tubule) and outer medulla (late proximal tubule) are determined. The charge stoichiometries of these transporters are in good agreement with their sodium/glucose coupling ratios arguing against the possibility that glucose transport is coupled to ions other than sodium in these membranes.

Animals↗
PubMed1980

Morphology and ultrastructure of oral strains of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus.

Selected human oral and nonoral strains of the genera Actinobacillus and Haemophilus were examined by transmission and scanning electron microscopy. The strains examined were morphologically identical to recognized Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus, and Haemophilus paraphrophilus. By transmission electron microscopy, the cells were typically gram negative in morphology, with several strains possessing some extracellular ruthenium red-staining polymeric material. Numerous vesicular structures, morphologically identical to lipopolysaccharide vesicles, were seen to originate from and be continuous with the surface of the outer membrane. Large numbers of these vesicles were also found in the external environment. Scanning electron microscopic observations revealed that both actinobacilli and haemophili possessed surface projections and an amorphous surface material which connected and covered adjacent cells.

Actinobacillus↗
PubMed1974

Transport studies in bacterial membrane vesicles.

The use of bacterial membrane vesicles as an experimental system for the study of active transport has been discussed. Vesicles are prepared from osmotically sensitized bacteria, and consist of osmotically intact, membranebound sacs without internal structure. They retain litle or no cytoplasm. Under appropriate conditions, these vesicles catalyze the transport of a variety of solutes at rates which are comparable, in many cases, to those of intact cells. Two general types of transport systems have been elucidated in the vesicle system: (i) group translocation systems which catalyze vectorial covalent reactions; and (ii) respirationlinked transport systems that catalyze the active transport of a whole range of metabolites against an electrochemical or osmotic gradient. In E. coli membrane vesicles, the respiration-linked transport systems are coupled primarily to the oxidation of (D)-lactate to pyruvate, catalyzed by a flavin-linked, membrane-bound (D)-lactate dehydrogenase which has been purified to homogeneity. Electrons derived from (D)-lactate or certain artificial electron donors are transferred to oxygen by means of a membrane-bound respiratory chain, and respiration is coupled to active transport within a segment of the respiratory chain between the primary dehydrogenase and cytochrome. b(l). The great majority of the individual membrane vesicles in the population catalyze active transport, and the generation or hydtolysis of ATP is not involved. Under anaerobic conditions, fumarate or nitrate can be utilized in place of oxygen as terminal electron acceptors. With the exception that (D)-lactate is not always the most effective electron donor for active transport, vesicles prepared from a number of other organisms catalyze transport in a similar manner. Fluorescent dansylgalactosides are useful molecular probes of active transport in the vesicle system. These compounds are competitive inhibitors of beta-galactoside transport, but are not transported themselves. Fluorescence studies indicate that the lac carrier protein constitutes approximately 3 to 6 percent of the total membrane protein, and that it is not accessible to the external medium unless the membrane is "energized." Thus, energy is coupled to one of the initial steps in the transport process. Studies with a photoaffinity-labeled galactoside provide independent support for this conclusion. When membrane vesicles prepared from a (D)-lactate dehydrogenase mutant of E. coli are treated with (D)-lactate dehydrogenase, the enzyme binds to the vesicles and they regain the capacity to catalyze (D)-lactate oxidation and (D)-lactate-dependent active transport. The maximal specific transport activity obtained in the reconstituted system is similar in magnitude to that of wildtype vesicles. Titration studies with dansylgalactoside demonstrate that there is at least a seven- to eightfold excess of lac carrier protein relative to (D)-lactate dehydrogenase. Evidence is presented indicating that the enzyme is bound to the inner surface of native membrane vesicles and to the outer surface of reconstituted vesicles, and that the flavin coenzyme moiety is critically involved in binding. Possible mechanisms of respirationlinked active transport are discussed.

Anaerobiosis↗
PubMed1975

Ultrastructural study of separated cell and acrosomal membranes from bull spermatozoa.

Ejaculated bull spermatozoa were washed and incubated with a cationic detergent, Hyamine 2389, and the material removed was centrifuged on a three-step sucrose gradient. Five different bands were obtained, three of which contained cell and acrosomal membranes and also acrosomal material. The first of these, band III, was composed of two parts. The lower part contained U-shaped membrane profiles originating from the outer acrosomal membrane, acrosomal material attached to them, and vesicles of different sizes. The upper part, in addition to various vesicles (probably formed from cell membrane), contained acrosomal vesicles arranged in the form of aggregates or caps. The latter vesicles were formed by fusion and vesiculation of the cell and outer acrosomal membranes with tightly bound acrosomal material. Band IV was uniform and comprised various round vesicles with a smooth membrane, which had a typical unit-membrane structure. There were obviously formed from the cell membrane. The fifth band, in the saline portion with material unsedimented in the sucrose, included small vesicles and membrane fragments, the origin of which was obscure. The solubilized material was also left in this fraction.

Acrosome↗
PubMed2000

Dopamine release from pharmacologically distinct storage pools in rat striatum following stimulation at frequency of neuronal bursting.

The increase of dopamine overflow in the rat caudate and nucleus accumbens following repeated stimulation of the median forebrain bundle (MFB) at short intervals and the role of alpha-methyl-p-tyrosine (AMPT) and reserpine sensitive storage pools in evoked dopamine overflow were investigated by in vivo voltammetry. In contrast to stimulation at 30-s intervals and longer, stimulation of the MFB at 5-s intervals led to increased dopamine release following each consecutive stimulation. This effect was much larger in the caudate than in the nucleus accumbens. We consider that the increase in dopamine release is due to translocation of dopamine from a reserpine-sensitive storage pool and this accounts for the increase of the rate of refilling of the readily releasable pool. The shorter the intervals between stimulation and the higher the frequency (with a plateau at 30 Hz), then the greater the fraction of dopamine which originates from the reserpine-sensitive storage pool. Exocytotic release of dopamine from the AMPT-sensitive storage pool does not seem to depend on the intervals between stimulation. We propose that the vesicles in presynaptic dopaminergic terminals near the outer membrane are more sensitive to AMPT. Distantly located vesicles have a relatively higher sensitivity to reserpine. Experiments using repeated stimulation at as low a frequency as 10-20 Hz, revealed that this phenomenon may take place under physiological conditions following bursting of dopamine neurones.

Animals↗
PubMed2001

Hydrogenosome morphological variation induced by fibronectin and other drugs in Trichomonas vaginalis and Tritrichomonas foetus.

The hydrogenosome is a spherical organelle, found in some anaerobic protozoa, which participates in ATP and molecular hydrogen formation. The morphological alterations in hydrogenosomes induced by fibronectin, hydroxyurea and cytochalasin B in Trichomonas vaginalis and Tritrichomonas foetus are presented. We demonstrate that, under experimental conditions, the hydrogenosome presents a high diversity in size and shape, suggesting a mechanism that seems to compensate for the stress provoked by drugs. The following experimental procedures were used: (1) fibronectin-mediated endocytic activity, (2) 4 mM hydroxyurea for 15 h, and (3) 10 microg cytochalasin B/ml in the culture medium. The main alterations observed in hydrogenosomes were: (1) formation of giant hydrogenosomes, (2) presence of internal membranes, (3) increased diversity of non-spherical forms, some of them bizarre, (4) presence of sub-compartments in the matrix, as vesicles, (5) presence of ribosome-like particles on the outer hydrogenosomal membrane, (6) enlargement of the peripheral vesicle, and (7) continuity with membrane profiles.

Animals↗
PubMed1988

Arginyl and histidyl groups are essential for organic anion exchange in renal brush-border membrane vesicles.

The effect of side chain modification on the organic anion exchanger in the renal brush-border membrane was examined to identify what amino acid residues constitute the substrate binding site. One histidyl-specific reagent, diethyl pyrocarbonate (DEPC), and 2 arginyl-specific reagents, phenylglyoxal and 2,3-butanedione, were tested for their effect on the specifically mediated transport of p-amino[3H]hippurate (PAH), a prototypic organic anion. The specifically mediated transport refers to the difference in the uptake of [3H]PAH in the absence and presence of a known competitive inhibitor, probenecid, and was examined in brush-border membrane vesicles isolated from the outer cortex of canine kidneys. The experiments were performed utilizing a rapid filtration assay. DEPC, phenylglyoxal, and 2,3-butanedione inactivated the specifically mediated PAH transport, i.e. probenecid inhibitable transport with IC50 values of 160, 710, and 1780 microM, respectively. The rates of PAH inactivation by DEPC and phenylglyoxal were suggestive of multiple pseudo first-order reaction kinetics and were consistent with a reaction mechanism whereby more than 1 arginyl or histidyl residue is inactivated. Furthermore, PAH (5 mM) did not affect the rate of phenylglyoxal inactivation. In contrast, PAH (5 mM) affected the rate of DEPC inactivation. The modification by DEPC was specific for histidyl residues since transport could be restored by treatment with hydroxylamine. The results demonstrate that histidyl and arginyl residues are essential for organic anion transport in brush-border membrane vesicles. We conclude that the histidyl residue constitutes the cationic binding site for the anionic substrate, whereas the arginyl residue(s) serves to guide the substrate to or away from the histidyl site.

Aldehydes↗
PubMed2000

Structure, function, and regulation of group V phospholipase A(2).

The hydrolysis of membrane phospholipid by phospholipase A(2) (PLA(2)) is a key step in the production of inflammatory eicosanoids. Recent cell studies have shown that secretory group V PLA(2) (gVPLA(2)) is involved in agonist-induced eicosanoid biosynthesis in mouse P388D1 cell line, mast cells, and transfected HEK 293 cells. gVPLA(2) is homologous to other group II PLA(2) family members but has distinctive enzymatic properties, including its activity to effectively hydrolyze phosphatidylcholine (PC) vesicles and the outer plasma membrane of mammalian cells. Mutational studies showed that gVPLA(2) has a unique structure that allows effective binding to PC membranes and efficient catalysis of an active-site-bound PC substrate. Thanks to this unique structure and activity, exogenously added gVPLA(2) can induce the eicosanoid biosynthesis in unstimulated inflammatory cells, including human neutrophils and eosinophils, suggesting that it might be able to trigger inflammatory responses under certain physiological conditions. Extensive structure-function and cell studies showed that gVPLA(2) could act directly on the outer plasma membranes of neutrophils and eosinophils. The release of fatty acids and lysophospholipids from the cell surfaces induces the translocation and activation of cytosolic PLA(2) and 5-lipoxygenase, resulting in the leukotriene synthesis. In case of neutrophils, induction of leukotriene B(4) synthesis by gVPLA(2) leads to the phosphorylation of cytosolic PLA(2) by a leukotriene B(4) receptor and MAP kinase-mediated mechanism. Finally, heparan sulfate proteoglycans in neutrophils appear to play a role of internalizing and degrading the cell surface-bound gVPLA(2) to protect the cells from extensive lipolytic damage.

Amino Acid Sequence↗
PubMed2000

Neuronal distribution and subcellular localization of HCNP-like immunoreactivity in rat small intestine.

A novel peptide, hippocampal cholinergic neurostimulating peptide (HCNP), originally purified from young rat hippocampus, affects the development of specific cholinergic neurons of the central nervous system in vitro. In this study, HCNP-like-immunoreactive nerve processes and nerve cell bodies were identified by electron microscopic immunocytochemistry in the rat small intestine. Labeled nerve processes were numerous in the circular muscle layer and around the submucosal blood vessels. In the submucosal and myenteric plexuses, some HCNP-like-immunopositive nerve cell bodies and nerve fibers were present. The reaction product was deposited on the membranes of various subcellular organelles, including the rough endoplasmic reticulum, Golgi saccules, ovoid electron-lucent synaptic vesicles in axon terminals associated with submucosal and myenteric plexuses, and the outer membranes of a few mitochondria. The synaptic vesicles of HCNP-like positive terminals were 60-85 nm in diameter. The present data provide immunocytochemical evidence that HCNP-like-positive nerve cell bodies and nerve fibers are present in the submucosal and myenteric plexuses of the rat small intestine. An immunohistochemical light microscopic study using mirror-image sections revealed that in both the submucosal and myenteric ganglia, almost all choline acetyltransferase (ChAT)-immunoreactive neurons were also immunoreactive for HCNP. These observations suggest (i) that HCNP proper and/or HCNP precursor protein is a membrane-associated protein with a widespread subcellular distribution, (ii) that HCNP precursor protein may be biosynthesized within neurons localized in the rat enteric nervous system, and (iii) that HCNP proper and/or HCNP precursor protein are probably stored in axon terminals.

Animals↗
PubMed1974

Heterogeneity in lipid composition of the outer membrane and cytoplasmic membrane and cytoplasmic membrane of Pseudomonas BAL-31.

The outer membranes and cytoplasmic membranes of the marine bacterium Pseudomonas BAL-31 were separated by washing the cells three times in 0.5 M NaCl and twice in 0.5 M sucrose. Electron microscopy during the removal of membranes revealed that the outer membranes fragmented in a regular manner to give rise to fairly uniform vesicles measuring approximately 140 nm in diameter. Isolated outer membranes had a buoyant density in sucrose of 1.230 g per cm(3), whereas the cytoplasmic membranes had a density of 1.194 g per cm(3). The removal of the outer membrane during the application of this procedure was monitored by measuring the release of 2-keto-3-deoxyoctulosonic acid and phospholipid. The cells lost 85.5% of their 2-keto-3-deoxyoctulosonic acid and 47.3% of their phospholipid during this treatment. Complete recovery of outer membrane material could be achieved. The removal of 25.5% of the 2-keto-3-deoxyoctulosonic acid and 0.9% of the phospholipid rendered the cells sensitive to lysis with Triton X-100. The phospholipid composition of the outer membrane was calculated to be 78.9% phosphatidylethanolamine and 16.1% phosphatidylglycerol. The phospholipid composition of the cytoplasmic membrane proved to be 71.5% phosphatidylethanolamine and 23.5% phosphatidylglycerol. The fatty acid composition was also found to be quantitatively heterogeneous between the two membranes.

Autoradiography↗
PubMed2004

Inhibition of hemagglutinating activity by monoclonal antibody against Porphyromonas gingivalis 40-kDa outer membrane protein.

Periodontitis is a chronic inflammatory disease of periodontal tissues that results in alveolar bone loss, and Porphyromonas gingivalis, which has a high hemagglutinating activity, has been implicated as an important pathogen in the development of periodontitis. This bacterium has a high hemagglutinating activity. We previously succeeded in gene cloning the 40-kDa outer membrane protein (OMP) from P. gingivalis 381. Although recombinant (r) 40-kDa OMP itself did not show hemagglutinating activity, its polymeric form, constructed with a cross-linking reagent, significantly expressed that activity. Furthermore, an affinity-purified antibody against r40-kDa OMP inhibited the hemagglutinating activity of P. gingivalis vesicles. In the present study, in order to clarify the pathological role of 40-kDa OMP and develop passive immunotherapy, we examined the inhibitory effect of monoclonal antibodies (MAbs) against r40-kDa OMP on the hemagglutinating activity of P. gingivalis vesicles. The MAbs reacted with r40-kDa OMP, the outer membrane fraction, vesicles, and P. gingivalis cell extracts, and significantly inhibited the hemagglutinating activities of the polymeric r40-kDa OMP as well as of P. gingivalis vesicles. These findings suggest that MAbs against 40-kDa OMP may be useful for the development of passive immunotherapy and for assessing treatment for periodontal diseases caused by P. gingivalis infection.

Animals↗
PubMedDate not supplied

[Utilization of different microbiological markers in the study of Haemophilus influenzae].

The present study includes 178 Haemophilus influenzae strains isolated in different pediatric hospitals from Havana, Cuba, during 1991-1994, associated to divers infections (meningitis, respiratory sepsis, primary bacteremia). A combination of various typing and subtyping methods was used as epidemiological markers: serotyping (slide agglutination with diagnostical serum a-f and latex agglutination), biotyping according to Killian's procedures (by determination of indole production, urease and ornithine decarboxylase activity), subtyping by fermentative profiles according to Roberts' methods (glucose, maltose, xylose and fructose) and outer membrane protein profile subtyping (vesicles extraction by a modified Barenkamp's method, analysis by lineal and gradient SDS-PAGE and assessment according to our own classification system). Serotype b was identified in 89.3%, biotype I was the most frequent (79.1%), other biotypes (II, III, IV and V) were also identified. Fermentative profile D (glucose, maltose, xylose and fructose positive) was the most frequent (52.8%) while profile G (glucose, maltose, xylose positive and fructose negative) represented 20.2%. Other known profiles were present. PA2 (33.7%) was the most frequent OMP subtype. Even though 11 different protein subtypes were found, the 77.5% of the strains were located in only three OMP electrophoretic subtypes (PA2, PC1, LA2).

Agglutination Tests↗
PubMed1992

Decreased sodium dependent D-glucose transport across renal brush-border membranes in cis-diamminedichloride platinum induced acute renal failure.

Na-coupled D-glucose transport in rabbits with cis-diamminedichloride platinum (CDDP; cisplatin) induced acute renal failure (ARF) has been studied. ARF occurred at 3 days after injection of CDDP (3 mg/kg i.v.). Na-coupled D-glucose transport into brush-border membrane vesicles (BBMV) from both outer cortex (OC) and outer medulla (OM) of ARF rabbits under zero-trans condition was decreased. Increased Km (i.e., decreased affinity of transport carrier for D-glucose) in OC and decreased Vmax (i.e., decreased number of glucose carrier) in OM were observed in CDDP-induced ARF rabbits. Decrease glucose transport was also observed under equilibrium exchange condition. Intravesicular volume of BBMV from OC and OM of ARF rabbits was decreased. In homogenate and BBMV from OC and OM of ARF rabbits, activities of gamma-glutamyl transpeptidase and alkaline phosphatase (marker enzymes of brush-border membrane) were decreased. Activities of succinate dehydrogenase, glucose-6-phosphatase, and Na-K ATPase (marker enzymes of mitochondria, endoplasmic reticulum, and basal lateral membrane, respectively) were not affected by CDDP administration. These results suggested that one of the main target sites of CDDP in kidney is brush-border membrane (BBM) along the proximal tubule, that is, not only Na-coupled D-glucose transport carrier protein but also other proteins in BBM.

Acute Kidney Injury↗
PubMed1988

Plasma membrane vesicles of opposite sidedness from soybean hypocotyls by preparative free-flow electrophoresis.

Absolute orientations (sidedness) of plasma membrane vesicles obtained in highly purified fractions by preparative free-flow electrophoresis and by aqueous two-phase partition were determined based on ATPase latency and morphological criteria. Free-flow electrophoresis yielded two plasma membrane fractions. One, the least electronegative and designated fraction ;E,' was pure plasma membrane. The other, more electronegative and designated fraction ;C,' was heavily contaminated by various other cellular membranes. Plasma membrane vesicles from both fraction C and fraction E partitioned into the upper phase with aqueous two-phase partitioning. Purified plasma membrane obtained from microsomes by two-phase partition (upper phase) when subjected to free-flow electrophoresis also yielded two fractions, one fraction co-migrated with fraction C and another fraction co-migrated with fraction E. Both fractions exhibited an ATPase activity sensitive to vanadate and insensitive to nitrate and azide. ATPase activity was used as a structure-linked latency marker for the inner membrane surface. Concanavalin A binding (linked to peroxidase) was used as an imposed electron microscope marker for the outer membrane surface. Fraction E vesicles showed low ATPase latency (two-fold or less) and weak reactivity with concanavalin A peroxidase. In contrast, fraction C vesicles were characterized by much greater latencies upon detergent treatment (sevenfold) and a strong reaction with concanavalin A peroxidase. Two-phase partition as the initial procedure for plasma membrane isolation, yielded mixtures of vesicles of both inside out and right-side out orientation. Free-flow electrophoresis resolved the plasma membrane isolates into vesicles from fraction C which were right-side out (cytoplasmic side in), and vesicles from fraction E which were wrong-side out (cytoplasmic side out). Therefore, the two methods used in series, provided highly purified membrane preparations of apparently homogenous vesicles of opposite known absolute orientations.

Journal Article↗
PubMed1989

Activation of K+ channels in renal medullary vesicles by cAMP-dependent protein kinase.

ADH, acting through cAMP, increases the potassium conductance of apical membranes of mouse medullary thick ascending limbs of Henle. The present studies tested whether exposure of renal medullary apical membranes in vitro to the catalytic subunit of cAMP-dependent protein kinase resulted in an increase in potassium conductance. Apical membrane vesicles prepared from rabbit outer renal medulla demonstrated bumetanide- and chloride-sensitive 22Na+ uptake and barium-sensitive, voltage-dependent 86Rb+ influx. When vesicles were loaded with purified catalytic subunit of cAMP-dependent protein kinase (150 mU/ml), 1 mM ATP, and 50 mM KCl, the barium-sensitive 86Rb+ influx increased from 361 +/- 138 to 528 +/- 120 pM/mg prot.30 sec (P less than 0.01). This increase was inhibited completely when heat-stable protein kinase inhibitor (1 microgram/ml) was also present in the vesicle solutions. The stimulation of 86Rb+ uptake by protein kinase required ATP rather than ADP. It also required opening of the vesicles by hypotonic shock, presumably to allow the kinase free access to the cytoplasmic face of the membranes. We conclude that cAMP-dependent protein kinase-mediated phosphorylation of apical membranes from the renal medulla increases the potassium conductance of these membranes. This mechanism may account for the ADH-mediated increase in potassium conductance in the mouse mTALH.

Adenosine Triphosphate↗
PubMed1984

Temperature dependence of action of polymyxin B on Escherichia coli.

The temperature dependence of the action of polymyxin B on Escherichia coli was studied by using K+, Ca2+, and tetraphenylphosphonium (TPP+) ion-selective electrodes. At room temperature (27 degrees C), Ca2+ was released immediately after addition of polymyxin, while the efflux of K+ occurred after 30 s. The rapid release of Ca2+ was not affected by incubation temperature, while the efflux of K+ was significantly lowered at temperatures below about 25-30 degrees C. The uptake of TPP+ also increased after polymyxin addition. The release of Ca2+ and the uptake of TPP+ supported the disruption of the outer membrane structure reported previously. In experiments with isolated membrane vesicles (the cytoplasmic membrane being exposed), the efflux of K+ was not delayed, but was lowered at temperatures below about 15-20 degrees C. This temperature range differed significantly from that of whole cells, and was interpreted as representing a difference in membrane fluidity between the outer and cytoplasmic membranes. The phase transition temperature of the outer membrane is known to be higher than that of the cytoplasmic membrane; and the temperature dependence of efflux of K+ from membrane vesicles was compatible with the phase transition temperature of liposomes prepared with phospholipids (not containing lipopolysaccharides) extracted from E. coli. Thus, it was speculated that, with whole cells, polymyxin molecules passed through the outer membrane at temperatures above the phase transition and reached the cytoplasmic membrane, increasing its K+ permeability. The mechanism of the permeability change is discussed in terms of deformation of the cytoplasmic membrane structure induced by polymyxin molecules.

Calcium↗
PubMed2001

Alpha-synuclein immunoreactivity in normal and neoplastic Schwann cells.

Alpha-synuclein is known to play an important role in several neurodegenerative diseases. Moreover, it is expressed in central nervous system neuronal tumors, and another member of the synuclein family, gamma-synuclein, is overexpressed in breast and ovarian carcinomas. However, the expression of alpha-synuclein has not been reported hitherto in the peripheral nervous system (PNS). In the present study, we investigated normal PNS tissue and schwannomas in human postmortem and biopsy samples using both immunocytochemistry and immunoelectron microscopy with antibodies against alpha-, beta- and gamma-synuclein. In normal PNS tissue, Schwann cells, but not axons or myelin, were immunopositive for alpha-synuclein. In schwannomas, almost all of the tumor cells showed diffuse cytoplasmic staining for alpha-synuclein (30 cases). Ultrastructurally, alpha-synuclein immunoreactivity was found in the cytoplasm of normal and neoplastic Schwann cells, in association with the plasma membrane, ribosomes, rough endoplasmic reticulum, small vesicles, Golgi apparatus and the nuclear outer membrane. No beta- or gamma-synuclein immunoreactivity was found in those cells. These results indicate that in the PNS, alpha-synuclein is a useful marker of Schwann cells and that it is not involved in tumorigenesis.

Aged↗
PubMed1980

Some characteristics of the outer membrane material released by growing enterotoxigenic Escherichia coli.

The high-molecular-weight material released into the medium by Escherichia coli AP1, an enterotoxigenic strain of porcine origin, has been isolated and resolved into two clearly distinct fractions, based on sucrose density gradient and differential centrifugation, chemical analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and freeze-fracture electron microscopy. These two fractions, referred to as "medium vesicles" and "medium lipopolysaccharides", were compared with the cellular outer and cytoplasmic membranes, the periplasmic fraction, and the cytoplasmic fraction. The medium vesicles closely resembled outer membrane and accounted for 3 to 5% of the total cellular outer membrane. They contained most of the heat-labile enterotoxin (LT) activity released into the medium by E. coli AP1. The medium lipopolysaccharide consisted mostly of lipopolysaccharide and a small amount of outer membrane and contained relatively little LT activity. Based on experiments with E. coli K-12 strains, in which about 5% of the newly synthesized outer membrane is lost from areas of outer membrane synthesis, it is proposed that enterotoxigenic E. coli strains release LT as part of such newly synthesized outer membrane fragments and that released outer membrane fragments may function as physiologically significant LT carriers.

Centrifugation, Density Gradient↗