Biochemical characterization of human umbilical vein endothelial cell membrane bound acetylcholinesterase

Acetylcholinesterase is an enzyme whose best-known function is to hydrolyze the neurotransmitter acetylcholine. Acetylcholinesterase is expressed in several noncholinergic tissues. Accordingly, we report for the first time the identification of acetylcholinesterase in human umbilical cord vein endothelial cells. Here we further performed an electrophoretic and biochemical characterization of this enzyme, using protein extracts obtained by solubilization of human endothelial cell membranes with Triton X-100. These extracts were analyzed under polyacrylamide gel electrophoresis in the presence of Triton X-100 and under nondenaturing conditions, followed by specific staining for cholinesterase or acetylcholinesterase activity. The gels revealed one enzymatically active acetylcholinesterase band in the extracts that disappeared when staining was performed in the presence of eserine (an acetylcholinesterase inhibitor). Performing western blotting with the C-terminal anti-acetylcholinesterase IgG, we identified a single protein band of approximately 70 kDa, the molecular mass characteristic of the human monomeric form of acetylcholinesterase. The western blotting with the N-terminal anti-acetylcholinesterase IgG antibody revealed a double band around 66-70 kDa. Using the Ellman's method to measure the cholinesterase activity in human umbilical vein endothelial cells, regarding its substrate specificity, we confirmed the existence of an acetylcholinesterase enzyme. Our studies revealed a predominance of acetylcholinesterase over other cholinesterases in human endothelial cells. In conclusion, we have demonstrated the existence of a membrane-bound acetylcholinesterase in human endothelial cells. In future studies, we will investigate the role of this protein in the endothelial vascular system.     

Purification and properties of the membrane-bound acetylcholinesterase from adult rat brain

The membrane-bound acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) from adult rat brain has been purified to homogeneity using sequential affinity chromatography on Con A-Sepharose and on dimethyl-aminoethylbenzoic acid-Sepharose 4B followed by DEAE-cellulose chromatography. The yield of the purified enzyme (specific activity: 3068 U/mg protein) is higher than 50%. Polyacrylamide gel electrophoresis in the presence of Triton X-100 gives only one band with acetylcholinesterase activity. With the exception of electrofocusing and pore gradient electrophoresis, where a multiple band pattern was detected (which seems to be artefactual), the enzyme appears to be homogenous. Gel filtration and sucrose density gradient centrifugation in the presence of Triton X-100 give only one symmetrical peak, with a calculated molecular weight of 328 000. Since polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS) and mercaptoethanol gives only one band with a molecular weight of 74 500, a tetrametric structure can be postulated for the membrane-bound acetylcholinesterase from rat brain.     

Multiple forms of acetylcholinesterase from pig brain

1. A number of methods of solubilization of pig brain acetylcholinesterase (EC 3.1.1.7) were studied. The multiple enzymic forms of the resultant preparations were examined by polyacrylamide-gel electrophoresis. 2. Butanol extraction, Nagarase treatment and ultrasonication proved unsuitable as preparatory methods, but detergent treatment (Triton X-100, Triton X-100-KCl and lysolecithin) gave good yields. 3. Separation of soluble enzyme in three systems of polyacrylamide-gel electrophoresis were compared and the relative advantages are discussed. 4. By using a 6% (w/v) gel and continuous buffer system two forms of acetylcholinesterase were detected in Triton X-100-solubilized enzyme, but the incorporation of a sample and spacer gel and a discontinuous buffer system resolved this into four components. The forms of the soluble enzyme extracted by different methods differed in mobility. 5. With gradient polyacrylamide-gel electrophoresis between two and six forms were detected, depending on the method used for extraction. The average molecular weights of the five forms most frequently found were 60000, 130000, 198000, 266000 and 350000. 6. Treatment of the Triton X-100-extracted enzyme with 2.5m-urea altered the pattern and evidence of dissociation was observed. 7. The results are discussed in the light of present theories on the molecular structure of acetylcholinesterase.     

Purification and characterization of amphiphilic trehalase from rabbit small intestine

Rabbit intestinal trehalase (alpha,alpha-trehalose glucohydrolase, EC 3.2.1.28) was solubilized with Triton X-100 and purified in the presence of EDTA. The purified enzyme was homogeneous on polyacrylamide gel electrophoresis in the presence of Triton X-100 or SDS. It showed amphiphilic properties on gel filtration. polyacrylamide gel electrophoresis, charge-shift electrophoresis and phenyl-Sepharose chromatography. Its molecular weight was estimated to be about 330 000 by gel filtration under nondenaturing conditions and in the presence of Triton X-100, the value being in satisfactory agreement with the sum of the weight of one Triton X-100 micelle and twice the molecular weight (105 000) of purified hydrophilic trehalase which had been deprived of the anchor segment. The two purified trehalases gave almost the same molecular weights (about 75 000) on SDS-polyacrylamide gel electrophoresis. These results suggest that intestinal trehalase consists of two subunits with a molecular weight of 75 000 and that its anchor segment is small (less than 5000). Triton X-100 extracts freshly prepared from intestinal microvilli essentially showed one form of trehalase, which behaved on phenyl-Sepharose and Con A-Sepharose chromatography in the same manner as purified amphiphilic trehalase.     

Multiple molecular forms of purified human erythrocyte acetylcholinesterase.

1. Human erythrocyte acetylcholinesterase was solubilized by Triton X-100 and purified by affinity chromatography to a specific activity of 3800 IU/mg of protein. The yield of the purified enzyme was 25--45%. 2. Gel filtration on Sepharose 4-B in the presence of Triton X-100 revealed one peak of enzyme activity with a Stokes' radius of 8.7 nm. Density gradient centrifugation in 0.1% Triton X-100 showed one peak of enzyme activity with an S4 value of 6.3S. 3. Isoelectric focusing in Triton X-100 resolved the enzyme into five molecular forms with isoelectric points of 4.55, 4.68, 4.81, 4.98 and 5.18. Upon incubation with neuraminidase the enzyme activity in the first four forms was decreased with a concommitant increase in activity in the form with the higher isoelectric point. 4. After removal of excess Triton X-100 on Bio-Gel HTP, polyacrylamide gel electrophoresis showed seven bands of protein and corresponding bands of enzyme activity. Density gradient centrifugation of the detergent-depleted enzyme at high ionic strength revealed five multiple molecular forms with S4 values of 6.3 S, 10.2 S, 12.2 S, 14.2 S and 16.3 S. At low ionic strength, higher aggregates were observed in addition to the other forms. Dodecylsulfate-polyacrylamide gel electrophoresis gave one subunit only with an apparent molecular weight of 80 000. 5. These results suggest that human erythrocyte acetylcholinesterase, solubilized by Triton X-100, exists in various forms differing in net charge but of apparently similar molecular dimensions. After removal of the detergent, forms with different molecular sizes are observed.     

Characterization of tumor cell membrane serine proteases by polyacrylamide gel electrophoresis

Studies in our laboratory have indicated that tumor cell membrane-bound proteases are responsible for the ability of tumor cells to lyse normal cells in vitro. In order to evaluate the tumor cell membrane enzymes, a purified tumor cell membrane preparation was prepared and the nonionic detergent Triton X-100 was used to extract active enzymes from the cell membranes. The solubilized membrane enzymes were then studied by Triton X-100 polyacrylamide gel electrophoresis under non-denaturing conditions. Using this technique the tumor cell membranes were shown to contain esterproteases that reacted with the substrates alpha-naphthyl acetate and naphthol-AS-aminocaproate. These esterproteases were inhibited by diisopropyl fluorphosphate and tosyl lysine chloromethyl ketone but not by tosylamide phenylethyl chloromethyl ketone, soybean trypsin inhibitor p-chloromercuribenzene sulfonic acid; N-ethylmaleimide choline iodide, alpha-1-anti-trypsin. NaF, epsilon-aminocaproic acid, ethylenediamine tetraacetic acid, or eserine. SBTI affinity chromatography of the tumor cell membrane extract revealed that some of the serine esterproteases bound to the SBTI column. The proteolytic activity of the tumor cell membrane extract and a fraction eluted from the SBTI affinity column was demonstrated using casein. We conclude that the tumor cell membranes contain previously undescribed serine proteases that are identifiable by their esterase activity and inhibitor profiles in polyacrylamide gels.     

Electrophoretically monodisperse cytochrome c oxidases

A discontinuous gradient polyacrylamide gel electrophoresis under nondenaturing conditions has been used to demonstrate monodispersity of procaryotic and eucaryotic cytochrome c oxidase preparations. Alkaline treated bovine enzyme which contains nine subunits as analysed by subsequent discontinuous SDS-polyacrylamide gel electrophoresis is a monodisperse dimer in 0.1% Triton X-100 and a monomer in 0.1% dodecyl maltoside. The Mr-values corrected for bound detergent are 286,000 in Triton X-100 and 152,000 in dodecyl maltoside respectively. The two-subunit bacterial cytochrome c oxidase of Paracoccus denitrificans is proved to be a monomer with a corrected Mr of 76,000 in both nonionic detergents Triton X-100 and dodecyl maltoside.     

Molecular forms of hippocampal acetylcholinesterase and their changes following septal lesions in the rat.

Changes of acetylcholinesterase activity and its molecular forms, extracted by Triton X-100 and separated by polyacrylamide gel electrophoresis, were studied in the rat hippocampus following septal lesions. Detection of acetylcholinesterase was made densitometrically. While the total activity of acetylcholinesterase was decreased, its molecular forms exhibited a different pattern of changes: the heavy forms were decreased, while the light ones were increased. The results support the view that different acetylcholinesterase molecular forms serve different regulatory mechanisms.     

Are soluble and membrane-bound rat brain acetylcholinesterase different?

Salt-soluble and detergent-soluble acetylcholinesterases (AChE) from adult rat brain were purified to homogeneity and studied with the aim to establish the differences existing between these two forms. It was found that the enzymatic activities of the purified salt-soluble AChE as well as the detergent-soluble AChE were dependent on the Triton X-100 concentration. Moreover, the interaction of salt-soluble AChE with liposomes suggests amphiphilic behaviour of this enzyme. Serum cholinesterase (ChE) did not bind to liposomes but its activity was also detergent-dependent. Detergent-soluble AChE remained in solution below critical micellar concentrations of Triton X-100. SDS polyacrylamide gel electrophoresis of purified, Biobeads-treated and iodinated detergent-soluble 11 S AChE showed, under non reducing conditions, bands of 69 kD, 130 kD and >250 kD corresponding, respectively, to monomers, dimers and probably tetramers of the same polypeptide chain. Under reducing conditions, only a 69 kD band was detected. It is proposed that an amphiphilic environment stabilizes the salt-soluble forms of AChE in the brain in vivo and that detergent-soluble Biobeads-treated 11 S AchE possess hydrophobic domain(s) different from the 20 kD peptide already described.Abbreviations used AChE acetylcholinesterase - BSA bovine serum albumin - ChE serum (butyryl) cholinesterase - ConA-Sepharose concanavalin A-Sepharose 4B - DMAEBA-Sepharose dimethylaminoethylbenzoic acid-Sepharose 4B - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - TMA tetramethylammonium chloride     

Purification of the acetylcholinesterase from human erythrocytes by affinity chromatography (author's transl)]

The acetylcholinesterase from human erythrocytes was released from the plasma membrane with 0.2% Triton X-100 at low ionic strength and purified by two affinity chromatography steps on Sepharose-bound m-[6-(6-amino-caproylamino)caproylamino]phenyltrimethyl-ammonium. The synthesis of the inhibitor is described. The purified, detergent-free acetylcholinesterase was obtained with a specific activity of 4270 U/mg (158000-fold purification) and a 28% yield. The enzyme is a glycoprotein and aggregates in the absence of Triton X-100 into higher molecular complexes. The molecular weight was estimated by sodium dodecylsulfate electrophoresis to be 80000 +/- 3000 in the presence of 2-mercapto-ethanol and 154000 +/- 6000 in its absence.     

Isolation and immunochemical characterization of fractions from membranes of Aspergillus fumigatus with protease activity

Two fractions exhibiting acid protease activity (AFPI and AFPII) were isolated by extraction of membrane vesicles of Aspergillus fumigatus with Triton X-100. These two fractions produced single bands in both polyacrylamide and sodium dodecyl sulfate polyacrylamide gel electrophoresis and showed apparent molecular weights of 73,000 and 43,000, respectively. Molecular weights determined by gel filtration in the absence and presence of Triton X-100 and sedimentation velocities in analytical ultracentrifugation indicated hydrophobic characteristics, since both fractions readily aggregated and complexed with Triton X-100; both exhibited elevated enzyme activities in the presence of Triton X-100. Carbohydrate content was 93% for AFPI and 85% for AFPII. The enzymatic fractions demonstrated different pH optima in the acid range as well as different temperature stabilities. Both protease fractions cross reacted in double immunodiffusion, while in crossed immunoelectrophoresis both demonstrated five precipitin peaks, each with similar patterns. AFPI demonstrated two additional precipitin peaks in crossed immunoelectrophoresis. As determined by crossed immunoaffinoelectrophoresis, the protease fractions demonstrated galactose and mannose residues. In biotin-avidin enzyme-linked immunosorbent assay both fractions reacted with allergic bronchopulmonary aspergillosis and aspergilloma sera. It can be concluded that two fractions with protease activity of A. fumigatus reported here may be of significance in Aspergillus-induced diseases.     

Purification of the insulin receptor from human placental membranes

Insulin receptors were purified from human placental microsomal membranes by solubilisation with Triton X-100 followed by Sepharose 6B chromatography, phosphate gradient elution from hydroxyapatite and affinity chromatography on concanavalin A-Sepharose. 2000-fold purification was achieved with 63% overall recovery. The purified receptor gave a single band on 3.75% polyacrylamide (0.1% Triton X-100) gel electrophoresis. On sodium dodecyl sulphate-polyacrylamide gel electrophoresis there was a major band at 75,000 and a minor band at 80,000 daltons. The purified receptor rechromatographed on Sepharose 6B with an apparent molecular weight of 300,000.     

Two-dimensional polyacrylamide gel electrophoresis of ribosomal proteins: improved resolution with Triton X-100

The nonionic detergent Triton X-100 binds in varying proportions to specific ribosomal proteins and decreases the relative mobility of these proteins during electrophoresis. When Triton X-100 binds to these ribosomal proteins in the first-dimension gel, the resolution of the ribosomal proteins in the second-dimension gel pattern is greatly improved. Maximum binding of Triton X-100 to the ribosomal proteins is dependent on pH, urea concentration, and the complete reduction of cysteine and methionine. After first-dimension electrophoresis the Triton X-100 in the gel does not interfere with the binding of sodium dodecyl sulfate to the ribosomal proteins and the molecular weight of these proteins can still be estimated directly from the second-dimension slab gel.     

Isolation and partial characterization of an amphiphilic 56-kDa fatty acid binding protein from rat renal basolateral membrane

We have identified a 56-kDa fatty acid binding protein in rat renal basolateral membrane and purified it by extraction in nonionic detergent (Triton X-100), followed by gel filtration, DEAE-cellulose chromatography, and affinity chromatography. The purified protein was homogeneous on polyacrylamide gel electrophoresis in the presence of Triton X-100 or SDS. It showed amphiphilic properties on gel filtration, polyacrylamide gel electrophoresis, and oleate-Sepharose 4B chromatography. Its molecular mass was estimated to be 56 kDa by SDS-polyacrylamide gel electrophoresis. The protein showed optimal binding activity at pH 7.5 and 37 degrees C. The apparent Kd for palmitic acid was 0.79 microM. It was immunologically clearly distinct from renal cytosolic fatty acid binding protein.     

Mechanism of activation of acetylcholinesterase in brain tissue homogenates by detergents]

The mechanisms of activation of acetylcholinesterase (AChE) in the homogenates of rat and frog forebrains and medullae oblongatae under effects of non--ionic detergents (Triton X-100 and Tw-en 80) were studied. Titration of the active centers of enzyme by the highly selective phosphoorganic inhibitor HD-42 showed that the inhibitor-induced activation is due to the appearance of previously masked active sites of the enzyme. Activation of AChE in the homogenates of rat brain medulla oblongata was caused by lysis of the structural elements of nervous tissue which were not destroyed by homogenization. Another mechanism of AChE activation by the detergents (frog brain homogenate) is the destruction of the vesicular membrane structures present in the homogenate with AChE centers located on the inner surface of the vesicles.     

Solubilization, purification, and characterization of succinate dehydrogenase from membranes of Mycobacterium phlei.

Succinate dehydrogenase (SDH) was solubilized from membranes of Mycobacterium phlei by Triton X-100 with a recovery of about 90%. The solubilized SDH was purified about 90-fold by Sephacryl S-300, DEAE-cellulose, hydroxylapatite, and isoelectric focusing in the presence of Triton X-100 with a 20% recovery. SDH was homogeneous, as determined by polyacrylamide gel electrophoresis in nondenaturing gels containing Triton X-100. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the enzyme revealed two subunits with molecular weights of 62,000 and 26,000. SDH is a flavoprotein containing 1 mol of flavin adenine dinucleotide, 7 to 8 mol of nonheme iron, and 7 to 8 mol of acid-labile sulfide per mol of protein. Using phenazine methosulfate and 2,6-dichloroindophenol as electron acceptors, the enzyme had an apparent Km of 0.12 mM succinate. SDH exhibited a sigmoidal relationship of rate to succinate concentration, indicating cooperativity. The enzyme was competitively inhibited by fumarate with a Ki of 0.15 mM. In the absence of Triton X-100, the enzyme aggregated, retained 50% of the activity, and could be resolubilized with Triton X-100 with full restoration of activity. Cardiolipin had no effect on the enzyme activity in the absence of Triton X-100, but it stimulated the activity by about 30% in the presence of 0.1% Triton X-100 in the assay mixture. Menaquinone-9(2H), isolated from M. phlei, had no effect on the enzyme activity either in the presence or absence of Triton X-100.     

Molecular forms of purified human erythrocyte membrane acetylcholinesterase investigated by crosslinking with diimidates.

Several molecular forms of human erythrocyte membrane acetylcholinesterase have been studied after crosslinking with bifunctional diimidates. The crosslinked products were analysed by centrifugation on linear sucrose density gradients containing Triton X-100. Molecular weights of covalently linked oligomers were estimated by sodium dodecylsulfate gel electrophoresis. It was shown that acetylcholinesterase crosslinked in absence of Triton X-100 consists of molecular forms built up by dimeric protomers. These dimers were identical with the enzymatically active species sedimenting with 6.5S in linear sucrose density gradients.     

Optimization of phenol extraction procedures for preparation of RNA from mammalian lymphoid organs

We have investigated the effect of different concentrations of Triton X-100 on the resolution of microgram amounts of different hemoglobin subunit polypeptides during electrophoresis in polyacrylamide gels containing acetic acid, urea, and Triton X-100. The results of these studies indicate that adequate concentrations of Triton X-100 facilitate the resolution of polymorphic globin chains and that this type of electrophoretic separation is technically much simpler and more sensitive than currently used methods. Using this method, known and previously undescribed types of α and β chains can be detected. Furthermore, polyacrylamide gel slabs containing a horizontal gradient of Triton X-100 permit the identification of different globin chains present in lysates of erythrocytes or erythrocyte precursors without prior purification of the hemoglobins.     

Binding of bacterial lipopolysaccharide to histocompatibility-2-complex proteins of mouse lymphocytes.

The membrane binding sites for lipopolysaccharide (LPS) were isolated by affinity chromatography of the solubilized membranes prepared from 125I-labeled mouse B-cells and T-cells on an affinity adsorbent prepared by coupling Salmonella minnesota R595 LPS to activated Sepharose 4B. The membrane proteins bound to the affinity adsorbent and eluted with 1.0% Triton X-100 were analyzed according to their mobility on polyacrylamide gel electrophoresis in sodium dodecylsulphate. These membrane proteins were further identified by immunoprecipitation with specific antisera. Immunoglobulins, possibly immunoglobulins M and D, were identified in the eluate from the B-cell membranes. The histocompatibility-2-complex proteins (H-2D, H-2K and Ia antigens) were also found to be binding sites for LPS on both B-cells and T-cells.     

Modification of a ferric enterobactin receptor protein from the outer membrane of Escherichia coli.

Modification of a ferric enterobactin receptor protein of Escherichia coli was observed upon incubation of either whole membranes or Triton X-100 solubilized outer membrane at 37°C. The modification was characterized by a change in mobility of the receptor band on SDS polyacrylamide gel electrophoresis and by a decreased binding capacity for ferric enterobactin. The rate of modification was affected by temperature and trypsin inhibitor, benzamidine. Ferric enterobactin inhibited the reaction in whole membrane. The modification affected the limited chymotrypsin digestion pattern of the receptor. The activity may represent a specific modification of the receptor, one possibly mediated by a membran-associated enzyme.