Molecular forms of Electrophorus acetylcholinesterase. Molecular weight and composition

Pressure-induced molten globule state of human acetylcholinesterase: structural and dynamical changes monitored by neutron scattering

We used neutron scattering to study the effects of high hydrostatic pressure on the structure and dynamics of human acetylcholinesterase (hAChE).

Association of tailed acetylcholinesterase to lipidic membranes in mammalian skeletal muscle

Tailed acetylcholinesterase (AChE) was studied in three subcellular membrane fractions of mouse skeletal muscle: a fraction enriched in isolated motor endplates (C), an extrasynaptic membrane fraction (A) and a microsomal fraction (S). In the (C) fraction, tailed asymmetric 16S AChE required high salt conditions to be extracted, while in (A) and (S) microsomal membranes, a collagenase sensitive 16S form, was extracted by detergent alone. This apparent "hydrophobic" property suggests that there is a pool of 16S AChE which is probably bound to lipidic membranes. The detergent extractable (DE) 16S AChE was not concentrated in motor endplate-rich regions and differential inhibition of external and internal AChE demonstrated that it could have both intra- and extracellular locations in the adult differentiated muscle fibres.

Extracellular matrix components involved in neuromuscular transmission and regeneration

The portion of a skeletal muscle fibre's basal lamina sheath that lies in the synaptic cleft at the neuromuscular junction contains a high concentration of certain molecules that distinguish it from non-junctional portions of the sheath. Among the molecules are acetylcholinesterase, which terminates the action of the transmitter, acetylcholine, on the postsynaptic membrane, and factors that direct differentiation at neuromuscular junctions regenerating after trauma. In this communication the evidence that acetylcholinesterase and synapse differentiation factors are associated with synaptic cleft basal lamina is reviewed and the results of current experiments aimed at characterizing these extracellular matrix molecules are described.

Acetylcholinesterase in the sea urchin Lytechinus variegatus: characterization and developmental expression in larvae

Acetylcholinesterase (AChE) in the echinoid Lytechinus variegatus has been characterized. Kinetic parameters V(max), K(m), K(ss), and b were 2594+/-1048 nmol ATCh hydrolyzed/min/mg tissue wet weight, 185+/-11 microM, 308+/-100 mM, and 0.2, respectively for the substrate ATCh and 17.8+/-6.87 nmol BTCh hydrolyzed/min/mg tissue wet weight, 654+/-424 microM, 36+/-31 mM, and 0.6, respectively for BTCh. Pharmacologic analyses were performed with four inhibitors of cholinesterases, physostigmine, BW284c51, ethopropazine, and iso-OMPA, and yielded IC(50) values of 106+/-4 nM, 718+/-118 nM, 2.57+/-0.6 mM, and >0.0300 M, respectively. Both kinetic and pharmacologic results confirmed the existence of AChE in larval L. variegatus. Dimeric and tetrameric globular forms (determined by velocity sedimentation on sucrose gradients) were present in L. variegatus larvae. Activity of AChE increased significantly as larvae progressed in development from embryos to eight-arm larvae. Acetylcholinesterase activity of F1 larvae derived from sea urchins collected from wild populations and of F1 larvae derived from sea urchins cultured in the laboratory and fed two different diets suggest that the nutritional and/or environmental history of the adult sea urchin affect the developmental progression of AChE activity in the F1 offspring.

An enzyme immunoassay for the quantification of plasma and intracellular lopinavir in HIV-infected patients

The protease inhibitor lopinavir (LPV; [1S-[1R*(R*), 3R*,4R*]]-N-[4-[[(2,6-dimethylphenoxy)-acetyl]amino]-3-hydroxy-5-phenyl-1-(phenylmethyl) pentyl] tetrahydro-alpha-(1-methylethyl)-2-oxo-1(2H)-pyrimide acetamide) is widely used in anti-human immunodeficiency virus (HIV) therapy. Knowledge of the plasma and intracellular concentrations of the drug would be useful for a better understanding of LPV action and for therapeutic monitoring. The aim of this study was to develop a sensitive and specific immunoassay for LPV in plasma and cells. Anti-LPV polyclonal antibodies were raised in rabbits using a synthetic LPV derivative coupled to keyhole limpet hemocyanin (KLH) as immunogen. The enzyme tracer was prepared by chemically coupling the LPV derivative with acetylcholinesterase. These reagents were used to develop a competitive enzyme immunoassay (EIA) performed in microtitration plates. The assay was performed on a minimum of 50 microl of plasma or 2 x 10(6) cells. It showed good precision and efficiency in as much as recovery from human plasma and cell extracts spiked with LPV ranged between 87% and 104%, with coefficients of variation of less than 10%. The limit of detection (LOD) was 100 pg/ml, i.e., a value at least 10 times lower than those currently achieved using previously described techniques. Cross-validation with high-performance liquid chromatography (HPLC) revealed a good correlation between methods (r2=0.96). Intracellular concentrations of LPV were measured in cultured human T lymphoblastoid cells (CEM). A pharmacokinetic analysis of plasma and intracellular LPV was performed on a healthy volunteer, and measurements were done in patients infected with HIV. The results obtained indicated a high intracellular/extracellular concentration ratio in cultured cells (19.3) but not in cells from HIV patients (1.3). In contrast, in peripheral blood mononuclear cells (PBMC) the accumulation of ritonavir (RTV) was six times higher than LPV. To date, this is the first reported immunoassay for LPV, and this method is sensitive enough for monitoring plasma and intracellular LPV levels in HIV-infected patients and for intracellular studies.

Quantification of plasma and intracellular levels of the HIV protease inhibitor ritonavir by competitive ELISA

The HIV protease inhibitor ritonavir (Norvir; ABT-578), currently used in combination with nucleoside analogs and other protease inhibitors in anti-HIV therapy, has previously been quantified by an HPLC procedure. Here, we report the first convenient one-step competitive ELISA for measuring plasma and intracellular ritonavir in HIV patients. Anti-ritonavir antibody was raised in rabbits using ritonavir-KLH conjugate as immunogen, and the enzymatic tracer was prepared by coupling the drug to acetylcholine esterase. Samples for analysis were first extracted with methanol. Bound/free separation was achieved in a microtiter plate previously coated with anti rabbit IgG monoclonal antibody. Fifty percent inhibition was observed at 1 ng/ml ritonavir and the method accurately and specifically detected as little as 3-4 ng/ml of plasma ritonavir as well as intracellular drug in the peripheral blood mononuclear cells of patients undergoing ritonavir therapy. Within-run and day to day coefficients of variation were below 10% and the drugs currently used in HIV therapy did not interfere with the test. The ELISA was applied to the measurement of plasma ritonavir and to the determination of the extracellular/intracellular drug level ratios in HIV patients receiving long-term multidrug therapy.

Cloning and expression of acetylcholinesterase from Electrophorus. Splicing pattern of the 3' exons in vivo and in transfected mammalian cells

We cloned and expressed a cDNA encoding acetylcholinesterase (AChE) of type T from Electrophorus electricus organs. When expressed in COS, HEK, and Chinese hamster ovary cells, the AChET subunits generated dimers and tetramers. The cells produced more activity at 27 than at 37 degrees C. The kinetic parameters of a recombinant enzyme, produced in the yeast Pichia pastoris, were close to those of the natural AChE. Analysis of genomic clones showed that the coding sequence is interrupted by an intron that does not exist in Torpedo and differs in its location from that observed in the mouse. This intron is preceded by a sequence encoding a non-conserved 29-amino acid peptide, which does not exist in Torpedo or mammalian AChEs. According to a three-dimensional model, this non-conserved peptide is located at the surface of the protein, opposite from the entry of the catalytic gorge; its deletion did not modify the catalytic parameters. Sequence analyses and expression of various constructs showed that the gene does not contain any H exon. We also found that splicing of transcripts in mammalian cells reveals cryptic donor sites in exons and acceptor sites in introns, which do not appear to be used in vivo.

Butyrylcholinesterase from chicken brain is smaller than that from serum: its purification, glycosylation, and membrane association

Applying a new four-step isolation procedure, we have purified butyrylcholinesterase (BChE) from chicken serum to homogeneity with more than 250 U/mg specific activity. The serum enzyme was used for producing monoclonal antibodies. These BChE-specific also recognize BChE from brain, and thus enabled us to isolate the enzymes from embryonic and adult brain that occur only in minute amounts. More than 50% of the brain BChE is membrane-bound. The catalytic and inhibition properties of brain BChE are similar to those of serum BChE. However on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the serum enzyme is represented by a double-band of 79/82 kDa, whereas the brain enzyme has a size of 74 kDa. Limited digestion of the serum and brain preparations by V8-protease leads to similar peptide patterns. Enzymatic deglycosylation shows that their core proteins consist of 59-kDa subunits and that the different molecular weights are due to different glycosylation patterns. The differently sized glycosylation parts of brain and serum BChE may indicate that they subserve different functions. Furthermore, the membrane-bound brain BChE can be solubilized by Pronase or protease K, but not by phosphatidylinositol-specific phospholipase C.

The effects of ethanol on the structural stability of acetylcholine receptor and the activity of various molecular forms of acetylcholinesterase

The actions of ethanol on the structural stability of acetylcholine receptor (AchR)-enriched membrane vesicles and the activity of various molecular forms of acetylcholinesterase (AchE) were investigated, using the receptor and the enzyme isolated from the electric organ of Torpedo californica. In the presence of ethanol up to 200 mM, the thermogram of AchR-enriched membranes exhibited no significant decrease in the temperature (td) of receptor transition at 57 degrees C, but a decrease in the enthalpy change (delta Hd) indicated a slight ethanol-induced structural perturbation. The presence of 12.5 nmol alpha-bungarotoxin also caused a decrease in delta Hd. A complete loss of the receptor transition was observed at a higher concentration 500 nmol of alpha-bungarotoxin and no recovery of the transition was found with the addition of 200 mM ethanol. The results suggested a noncompetitive interaction of ethanol with the receptor. In the presence of 200-1000 mM ethanol, the activity of two soluble forms of AchE, a higher (117 S) aggregate and a lower (10 S) aggregate was not significantly affected. Comparing the activity of these two aggregates over a wide concentration range of ethanol (200-2000 mM) revealed no obvious difference in the level of ethanol effect between them. However, after removal of ethanol, the higher aggregate form of AchE exhibited a greater recoverability of the activity, suggesting a possible slightly greater structure-functional stability for it. Studies of soluble AchE and membrane-bound AchE showed that the presence of 200 or 600 mM ethanol caused a greater level of inhibition in membrane-bound enzyme than in soluble enzyme, possible due to a disruption of protein-lipid interaction needed to maintain the conformation of membrane-bound AchE. Interestingly, at a much higher concentration of ethanol (2.0 M), membrane-bound AchE became more resistant to ethanol than did the soluble forms of AchE. In this case, the effective concentration of ethanol felt by the enzyme was expected to be less for membrane-bound AchE, owing to ethanol's solubility in lipids.

Monoclonal antibodies specific for the different subunits of asymmetric acetylcholinesterase from chick muscle

The asymmetric (20S) acetylcholinesterase (AChE, EC 3.1.1.7) from 1-day-old chick muscle, purified on a column on which was immobilised a monoclonal antibody (mAb) to chick brain AChE, was used to immunise mice. Eight mAbs against the muscle enzyme were hence isolated and characterised. Five antibodies (4A8, 1C1, 10B7, 7G8, and 8H11) recognise a 110-kilodalton (kDa) subunit with AChE catalytic activity, one antibody (7D11) recognises a 72-kDa subunit with pseudocholinesterase or butyrylcholinesterase (BuChE, EC 3.1.1.8) catalytic activity, and two antibodies (6B6 and 7D7) react with the 58-kDa collagenous tail unit. Those three polypeptides can be recognised together in the 20S enzyme used, which is a hybrid AChE/BuChE oligomer. Antibodies 6B6 and 7D7 are specific for asymmetric AChE. Four of the mAbs recognising the 110-kDa subunit were reactive with it in immunoblots. Sucrose density gradient analysis of the antibody-enzyme complexes showed that the anti-110-kDa subunit mAbs cross-link multiple 20S AChE molecules to form large aggregates. In contrast, there is only a 2-3S increase in the sedimentation constant with the mAbs specific for the 72-kDa or for the 58-kDa subunit, suggesting that those subunits are more inaccessible in the structure to intermolecular cross-linking. The 4A8, 10B7, 7D11, and 7D7 mAbs showed cross-reactivity to the corresponding enzyme from quail muscle; however, none of the eight mAbs reacted with either enzyme type from mammalian muscle or from Torpedo electric organ. All eight antibodies showed immunocytochemical localisation of the AChE form at the neuromuscular junctions of chicken twitch muscles.

An asymmetric form of muscle acetylcholinesterase contains three subunit types and two enzymic activities in one molecule

We have purified completely the principal asymmetric ("heavy") form of acetylcholinesterase (Ac-ChoEase; EC 3.1.1.7) from chick muscle (i.e., the synaptic form in the twitch muscle fibers) by using a monoclonal antibody that recognizes AcChoEase but not pseudocholinesterase (ChoEase; cholinesterase, EC 3.1.1.8). The purified protein exhibits catalytic and inhibition properties characteristic of AcChoEase and ChoEase and contains three distinct subunits of apparent sizes 110 kDa, 72 kDa, and 58 kDa in the ratio 2:2:1. The discovery of an AcChoEase/ChoEase hybrid asymmetric form has been further supported by (i) the identification of active site properties of AcChoEase in the 110-kDa subunit and of ChoEase in the 72-kDa subunit, (ii) the purification or precipitation of both activities together by, also, a ChoEase-specific monoclonal antibody, and (iii) evidence that all subunits are bound in the asymmetric forms by disulfide bonds. The 58-kDa subunit is the only one that is sensitive to digestion with purified collagenase; it carries the collagenous "tail" of the asymmetric form. A model is proposed for this form of AcChoEase.

Monoclonal antibodies against chicken brain acetylcholinesterase. Their use in immunopurification and immunochemistry to demonstrate allelic variants of the enzyme

Acetylcholinesterase (AChE) from 1-day chicken brain was enriched over 2000-fold by affinity chromatography using N-methylacridinium-Sepharose. This preparation was used to prepare monoclonal antibodies (mAb) directed against AChE, of which two were extensively characterised for further application. Both mAbs bound to the enzyme from the chicken with high affinity (Kd approximately 8 X 10(-10) M) and one mAb, in addition, recognised AChE from quail brain and muscle. Neither mAb cross-reacted with mammalian or fish AChE. Both mAbs recognised AChE in the endplate region of adult chicken skeletal muscle and bound with equal affinity to the three major oligomeric forms found in early ambryonic muscle. One mAb was used to immunopurify chicken brain AChE to homogeneity (over 12000-fold enrichment), with nearly complete recovery of the enzyme and without detectable proteolytic breakdown. The other mAb recognised AChE after immunoblotting and was used to screen crude brain extracts from individual chickens for allelic variations. Evidence is presented to show that two allelic forms occur, represented in SDS-PAGE by a doublet polypeptide of Mr approximately 110,000, this pattern is maintained after deglycosylation of the N-linked oligosaccharides. This variation was found throughout development and in both the brain and the muscle of individuals. We conclude that the gene encoding the catalytic subunit of chicken AChE is polymorphic with either one or two equally active alleles being expressed.

Soluble form of acetylcholinesterase from rabbit enterocytes: comparison of its molecular properties with those of the plasma membrane species

A soluble form of acetylcholinesterase was shown to be present in rabbit enterocytes. The enzyme was obtained from a high-speed supernatant (105,000 X g centrifugation) after homogenization of intestinal mucosa without detergent. It was shown to possess no obvious hydrophobic character and could be classified as a low-salt-soluble (LSS) acetylcholinesterase. Sucrose gradient centrifugation revealed a single enzyme species with a sedimentation coefficient of 3.9 +/- 0.2S. By gel filtration performed in HPLC the enzyme was eluted as a protein corresponding to an Mr of 72,000 +/- 3,000. It could be precipitated with concanavalin A by affinoelectrophoresis, but the catalytic activity was not affected by the lectin. Our results are consistent with a G1 globular form for this soluble acetylcholinesterase which differs very clearly from detergent-soluble forms also found recently in the plasma membranes of rabbit enterocytes.

Effect of membrane fluidity upon binding of Electrophorus acetylcholinesterase to lipid vesicles

A previous report (Watkins, M.S., Hitt, A.S. and Bulger, J.E. (1977) Biochem. Biophys. Res. Commun. 79, 640-647) has indicated that the asymmetric forms of Electrophorus acetylcholinesterase bind exclusively to sphingomyelin vesicles through interaction with the collagen-like 'tail' portion of the enzyme. We report here that acetylcholinesterase also binds to phosphatidylcholine vesicles containing saturated fatty acyl chains and to egg phosphatidylcholine vesicles containing cholesterol. This suggests preferential binding of acetylcholinesterase to membranes of lower fluidity. Surface charge of vesicles and density of zwitterionic lipid headgroups do not significantly affect binding of native acetylcholinesterase. The presence of chondroitin sulfate or hyaluronic acid slightly increases the binding of native acetylcholinesterase to sphingomyelin vesicles, while the presence of 1 M NaCl, bovine serum albumin, or tissue fractions enriched in basement membrane diminish binding. The dissociation constant for native acetylcholinesterase and sphingomyelin vesicles is (1.0-1.5) X 10(-7) M, as measured by a flotation binding assay. The globular, 11S form of acetylcholinesterase also binds to lipid vesicles, although not to the same degree as native acetylcholinesterase. This suggests that the collagen tail of the enzyme enhances binding, but is not essential for binding to occur. These results are consistent with the location of acetylcholinesterase on the surface of the postsynaptic plasma membrane in vivo.

Synthesis in vitro of precursors of the catalytic subunits of acetylcholinesterase from Torpedo marmorata and Electrophorus electricus

We translated poly(A-rich messenger RNA prepared from the electric organs of Electrophorus electricus and Torpedo marmorata in a reticulocyte lysate system. In the case of Electrophorus, which appears to contain only one type of acetylcholinesterase catalytic subunit, an anti-(Electrophorus acetylcholinesterase) antiserum precipitated a single 65-kDa polypeptide from the products translation obtained in vitro. In the case of Torpedo, where a number of distinct catalytic subunits corresponding to different fractions of the enzyme have been described, an anti-(Torpedo acetylcholinesterase) antiserum precipitated two main polypeptides, 61 kDa and 65 kDa, both of which could be displaced by unlabelled purified Torpedo acetylcholinesterase. Synthesis in vitro thus appears to produce a single type of precursor of the acetylcholinesterase catalytic subunit for Electrophorus, and at least two distinct precursors for Torpedo, suggesting that several mRNAs code for the catalytic subunits in the latter species.

Acetylcholinesterase of Schistosoma mansoni

Several molecular forms of acetylcholinesterase were obtained from Schistosoma mansoni homogenates by extraction in either low-salt buffer, high-salt buffer or detergent buffer. The low-salt soluble form amounts to 25% of the total activity. By contrast, the extract obtained in the presence of Triton X-100 possessed almost almost 3-fold higher enzymatic activity, most of it (86%) being retained in the soluble extract (100 000 X g). High-salt concentration (1 M NaCl) also has a solubilizing effect, but to a lesser extent (50%). Acetylcholinesterase can also be solubilized by treatment with a solution of 1% methylmannoside (40%). In the presence of non-ionic detergents, the enzyme behaves as monodisperse 8 S form. In the absence of detergent the low-salt soluble extract is polydisperse: it contains a 10 S and a 32 S component, the latter could represent high polymers. The molecular form released from tissue homogenate by treatment with alpha-methylmannoside is polydisperse: it contains a major 10 S and a minor 32 S component. Differences in sedimentation coefficient were observed among the enzymes extracted with detergent from the various life cycle stages of the parasite. The enzyme from the cercarial stage sediments as a single 8 S peak. The adult worm exhibits an additional acetylcholinesterase peak of 18 S representing approx. 30% of the total enzymatic activity. The molecular weight of the major 8 S species, as determined by gel filtration, is 450 000.

An immunological study of rat acetylcholinesterase: comparison with acetylcholinesterases from other vertebrates

We have examined the immunoreactivity of acetylcholinesterase from different vertebrate species with a rabbit antiserum raised against the purified rat brain hydrophobic enzyme (G4 form). We found no significant interaction with enzymes from Electrophorus, Torpedo, chicken, and rabbit. The antiserum reacted with acetylcholinesterases from the brains of the other mammalian species studied, with titers decreasing in the following order: rat = mouse greater than human greater than bovine. The serum was inhibitory with murine and human acetylcholinesterases, but not with the bovine enzyme. The inhibition was partially depressed in the presence of salt (e.g., 1 M NaCl). In those species whose acetylcholinesterase was recognized by the antiserum, both soluble and detergent-soluble fractions behaved in essentially the same manner, interacting with the same antibodies. The apparent immunoprecipitation titer was decreased in the presence of salt, and it did not make any difference whether NaCl was included in the solubilization procedure or added to the extracts. Both G1 and G4 forms of acetylcholinesterase in the soluble and detergent-soluble fractions were recognized by the antiserum, and in the case of the human enzyme, by monoclonal antibodies produced against human erythrocyte acetylcholinesterase. However, the monomer G1 showed a clear tendency to form smaller complexes and precipitate less readily than the tetramer G4. Although we cannot exclude the existence of significant differences between the various molecular forms of acetylcholinesterase, our results are consistent with the hypothesis that they all derive from the same gene or set of genes by posttranslational modifications.

Interactions with lectins indicate differences in the carbohydrate composition of the membrane-bound enzymes acetylcholinesterase and 5'-nucleotidase in different cell types

We have examined the interactions of the membrane-bound enzymes, 5'-nucleotidase and acetylcholinesterase from bovine tissues with lectins and shown that glycosylation contributes significantly to the polymorphism of these enzymes, in a tissue-specific manner. Lectins which bind 5'-nucleotidase also inhibit its catalytic activity to various degrees. We found different specificities with 5'-nucleotidases from various cell types: for example lymphocyte 5'-nucleotidase did not interact with wheat germ agglutinin, in contrast with 5'-nucleotidases from hepatocyte and caudate nucleus membranes. Treatment with glycohydrolases, alpha-D-mannosidase and neuraminidase, suggested that the latter enzymes possess sialic residues which are absent in the lymphocyte enzyme. Interactions of acetylcholinesterase with lectins were demonstrated by sedimentation analysis and binding to immobilized lectins, but its activity was generally not affected. A notable exception was lymphocyte acetylcholinesterase which was inhibited by the fucose-binding Ulex europeus agglutinin. This inhibition was relieved by alpha-L-fucose but not by alpha-D-fucose and reduced after treatment with alpha-L-fucosidase. In addition this enzyme differs from acetylcholinesterases from other tissues by its higher Km value, although it appears immunologically equivalent. The different forms of acetylcholinesterase from the same tissue may differ in their interactions with lectins. In muscle for example G4 carries carbohydrate chains of the complex type whereas G1 appears to possess only the high mannose type. We discuss the possible relationships between these forms.

Multiple molecular forms of acetylcholinesterase in the nematode Caenorhabditis elegans

Extracts of the nematode Caenorhabditis elegans contain five molecular forms of acetylcholinesterase (AChE) activity that can be separated by a combination of selective solubilization, velocity sedimentation, and ion-exchange chromatography. These are called form IA (5.2s), form IB (4.9s), form II (6.7s), form III (11.3s), and form IV (13.0s). All except form III are present in significant amounts in rapidly prepared extracts and are probably native; form III is probably derived autolytically from form IV. Most of forms IA and IB can be solubilized by repeated extractions without detergent, whereas forms II, III, and IV require detergent for effective solubilization and may therefore be membrane-bound. High salt concentrations are not required for, and do not aid in, the solubilization of these forms. For all forms, molecular weights and frictional ratios have been estimated by a combination of gel permeation chromatography and velocity sedimentations in both H2O and D2O. The molecular weight estimates range from 83,000 to 357,000 and only form II shows extensive asymmetry. The separated forms have been characterized with respect to substrate affinity, substrate specificity, inhibitor sensitivity, thermal inactivation, and detergent sensitivity. Judging by these properties, C. elegans is like other invertebrates in that none of its cholinesterase forms resembles either the "true" or the "pseudo" cholinesterase of vertebrates. However, internal comparison of the C. elegans forms clearly distinguishes forms IA, III, and IV as a group from forms IB and II; the former are therefore designated "class A" forms, the latter "class B" forms. Genetic evidence indicates that separate genes control class A and class B forms, and that these two classes overlap functionally. Several factors, including kinetic properties, molecular asymmetry, molecular size, and solubility, all suggest that a molecular model of the multiple cholinesterase forms observed in vertebrate electric organs probably does not apply in C. elegans. Potential functional roles and subunit structures of the multiple AChE forms within each C. elegans class are discussed.

Cholinergic traits in the neural crest: acetylcholinesterase in crest cells of the chick embryo

Previous work by our group has demonstrated that mesencephalic neural crest cells at an early stage of migration are able to synthesize acetylcholine (ACh). Acetylcholinesterase (AChE), the enzyme responsible for ACh degradation, was examined in neural crest cells of the chick embryo, using cytochemical and biochemical methods. Observations at the light microscope level showed that cholinesterase activity, identified as true AChE, was present at all axial levels in presumptive crest cells of the neural folds, soon after closure of the neural tube. Subsequently, AChE activity was found in cells of the individualized neural crest and in crest cells migrating at cephalic and trunk levels. Cell counts revealed that 88-94% of the total crest population was AChE-positive. Electron microscope observations indicated that the enzyme was confined to perinuclear and endoplasmic reticulum cisternae. The AChE of migrating mesencephalic neural crest cells was identified as the dimeric form (sedimentation coefficient 6.9 S) of the catalytic subunit. These results indicate that the specific AChE is present in the majority of neural crest cells all along the neural axis. Thus the ability to synthesize and degrade ACh is expressed at least in some neural crest cells at an early stage of development.

Comparative affinity chromatography of acetylcholinesterases from five vertebrate species

The efficacy of N-methylacridinium affinity chromatography in the purification of acetylcholinesterases from chicken, rat, calf and human brain and from the electric organ of the electric fish Torpedo marmorata has been investigated. Retention of the enzymes on the N-methylacridinium columns exceeded 90% in all instances except for the chicken enzyme, where 40-80% retention was observed depending on the acridinium concentration. Sucrose density gradient centrifugation profiles revealed no difference between the distribution of molecular forms in the crude extracts and in the partially purified fractions eluted from the columns by decamethonium iodide.

Changes in acetylcholinesterase molecular forms during the embryonic development of Torpedo marmorata

Multiple molecular forms of acetylcholinesterase from electric organ and electric lobe of Torpedo marmorata were examined at various developmental stages by sucrose density sedimentation. Four major forms were characterized by their apparent sedimentation coefficients of 6 S, 11 S, 13 S, and 17 S. Embryonic lobe possessed at early stages predominantly the 11 S form. With maturation the 17 S form became the most abundant. The early embryonic stages of the electric organ were characterized by predominating amounts of 6 S and 11 S forms. With differentiation of the postsynaptic membrane of the developing electrocytes, 13 S and 17 S forms replaced the slower-sedimenting forms. Concomitant with the formation of synaptic contacts, a transient increase in the 13 S form was followed by a dramatic accumulation of rapid-sedimenting 17 S form. The establishment of fully functional synapses was accompanied by an increase in the amount of the hydrophobic 6 S form. At birth, equal amounts of 6 S and 17 S form were found, with the other forms present in only trace amounts. The observed characteristic changes correlated with morphological and physiological events, indicating a close functional relationship between the accumulation of the 17 S form and synapse formation and the accumulation of the 6 S form and onset of function.

Serotonin-sensitive aryl acylamidase activity of platelet acetylcholinesterase

Serotonin-sensitive aryl acylamidase (AAA, EC 3.5.1.13) was purified to apparent homogeneity from sheep platelets by affinity chromatography and it was shown to be associated with the platelet acetylcholinesterase (AChE, EC 3.1.1.7). The basis for the association of the two enzymes was the following. Both enzyme activities co-eluted from the affinity columns with constant ratios of specific activities and percentage recoveries. Both enzymes co-migrated on gel electrophoresis. Both enzymes co-eluted during sepharose 6B gel filtration. Potent inhibitors of AChE such as bis(4-allyldimethyl ammoniumphenyl) pentan-3-one dibromide (BW 284C51), neostigmine and eserine also inhibited AAA potently. Both enzymes lost significant activity on treatment with deoxycholate or taurodeoxycholate and the loss could be partly restored by a mixture of phospholipids. The platelet AAA was specifically inhibited by serotonin and to a lesser extent by tryptamine but not by several other amines. It was also inhibited by acetylcholine and several of its analogues and homologues. It is suggested that in the platelets the two enzymes (AAA and AChE) are probably identical.

Comparison of the molecular forms of the cholinesterases in tissues of normal and dystrophic chickens

The levels and molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and pseudocholinesterase (psiChE, EC 3.1.1.8) were examined in various skeletal muscles, cardiac muscles, and neural tissues from normal and dystrophic chickens. The relative amount of the heavy (Hc) form of AChE in mixed-fibre-type twitch muscles varies in proportion to the percentage of glycolytic fast-twitch fibres. Conversely, muscles with higher levels of oxidative fibres (i.e., slow-tonic oxidative-glycolytic fast-twitch, or oxidative slow-twitch) have higher proportions of the light (L) form of AChE. The effects of dystrophy on AChE and psiChE are more severe in muscles richer in glycolytic fast-twitch fibres (e.g., pectoral or posterior latissimus dorsi, PLD); there is no alteration of AChE or psiChE in a slow-tonic muscle. In the pectoral of PLD muscles from older dystrophic chickens, however, the AChE forms revert to a normal distribution while the pesChE pattern remains abnormal. Muscle psiChE is sensitive to collagenase in a similar way as is AChE, thus apparently having a similar tailed structure. Unlike skeletal muscle, cardiac muscle has very high levels of psiChE, present mainly as the L form; AChE is present mainly as the medium (M) form, with smaller amounts of L and Hc. The latter pattern of AChE forms resembles that seen in several neural tissues examined. No alterations in AChE or psiChE were found in cardiac or neural tissues from dystrophic chickens.

Histochemical and biochemical demonstration of the molecular forms of acetylcholinesterase in peripheral nerve of rat

The molecular forms of AChE and their ultrastructural localization in the sciatic nerve and spinal ganglion were studied biochemically and histochemically. Our results suggest that the histochemical end-products due to the AChE activity are present in the cisternae of the RER of the perikaryon (4S,C form). The 6S,C and 10S,B' forms can be found in tubules and in vesicles inside the axon, while the 10S,B form may be present bound on the outer surface of the axolemma. The 16S,A form is localized in some intraaxonal cell organelles during transport. From the results presented it is inferred that the AChE from the perikaryon is transported both free in the cytoplasm and sequestered in a soluble form inside the tubules and vesicles, where a part of it is converted to the 10S,B' and 16S forms. When the AChE-active tubules are joined to the surface membranes, the 10S,B' form may be "extruded" (secreted) and bound to the outer surface of the unit membrane (10S,B form). Since both the 10S,B' and 16S forms are present in the tubules and vesicles, the regulatory process involved in the distribution of the 10S,B' AChE to the axon surface and of the 16S,A form to the axon terminal must be further examined.

Properties of 16S acetylcholinesterase from rat motor nerve skeletal muscle

Rat obturator nerve 16S acetylcholinesterase (16S AChE) was separated by sucrose gradient velocity sedimentation and compared to the 16S form of AChE similarly derived from endplate regions of anterior gracilis muscles. The 16S AChE from both tissues could only be extracted in high ionic strength buffer; as it aggregated under low ionic strength conditions. Treatment of nerve and muscle 16S AChE with purified collagenase, in the presence of calcium, caused an identical "shift" in the enzyme's sedimentation coefficient to 17.5S. Other properties which were also equivalent for 16S AChE from both tissue sources included: an excess substrate inhibition above 2 x 10(-3) M acetylcholine and Km of 1.6 x 10(-4) M, relative sensitivity to the specific inhibitors BW284C51 (I50 of 5 x 10(-8) M) and Iso-OMPA (I50 of 5 x 10(-4) M), and a half maximal thermal inactivation at 62.5 degrees C. These and additional results indicate that the 16S forms of AChE in both tissues are analogous molecules, which have a highly asymmetric conformation probably containing a collagen-like domain. The present findings are also consistent with the view that motor neurons provide at least a fraction of the 16S AChE present at the neuromuscular junction.

The quaternary structure of chicken acetylcholinesterase and butyrylcholinesterase; effect of collagenase and trypsin

Acetylcholinesterase (EC 3.1.1.7.; AChE) and butyrylcholinesterase (EC 3.1.1.8.; BuChE) from chicken muscle exist as sets of structurally homologous forms with very similar properties. The collagenase sensitivity and aggregation properties of the 'heavy' forms of both enzymes indicate that they possess a collagen-like tail, and their stepwise dissociation by trypsin confirms that they correspond to triple (A12) and double (A8) collagen-tailed tetramers. In addition to this dissociating effect, trypsin digests an important fraction of the catalytic units of AChE, in a progressive manner, removing as much as 30% of the enzyme's mass, without inactivation of the tetramers and of the tailed molecules. The trypsin-modified AChE forms closely resemble the corresponding mammalian AChE forms in their hydrodynamic properties. It is not known whether the trypsin-digestible peptides, which do not appear to be involved in the ionic or hydrophobic interactions of the enzymes, are a fragment of the catalytic subunit or whether they constitute distinct polypeptides.

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 homogeneous. 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 tetrameric structure can be postulated for the membrane-bound acetylcholinesterase from rat brain.

Acetylcholinesterase kinetics

Three mechanisms have been suggested to describe the inhibition of acetylcholinesterase (EC. 3.1.1.7) by an excess of acetylcholine. (i) Substrate inhibition occurs through the reaction of acetylcholine with acetylated enzyme. The deacetylation of this ternary complex is supposed to be completely inhibited. (ii) A ternary complex is formed as in (i). However, the deacetylation is not completely inhibited. (iii) A two-site-mechanism is discussed. Acetylcholine binds either to the active site or to the modifier site. Binding to the latter changes the activity of the active site. Steady state treatment was applied to (i)-(iii). A least squares fit led to catalytic parameters. It is demonstrated that mechanism (ii) is the most simple one which can describe satisfactorily the experimental data. Limits for a set rate constants are derived from the catalytic parameters. A numerical integration shows that the steady state approximation may be used even when the mechanisms are rather complex.

Characterization of multiple forms of acetylcholinesterase in electric organ of Torpedo marmorata

Three molecular forms of acetylcholinesterase can be isolated by velocity sedimentation from extracts of electric organ from Torpedo marmorata. Their apparent sedimentation coefficients are 6 S, 13 S and 17 S. Characteristic differences are found with regard to their solubilization properties. The 13 S and 17 S forms are extracted only in the presence of high salt concentrations. At low ionic conditions only a fraction of the 6 S form is solubilized. Quantitative recovery of this form can be achieved in the presence of Triton X-100 at concentrations of 0.5-1%. The relative ratio of the various forms changes during the development of the fish.

Modulation of the distribution of acetylcholinesterase molecular forms in a murine neuroblastoma x sympathetic ganglion cell hybrid cell line

Studies were carried out on the polymorphism of acetylcholinesterase (AChE, EC 3.1.1.7) in a neuroblastoma x sympathetic ganglion cell hybrid cell line (T28) and its parental clone (N18TG2). These cells contain the tetrameric (G4, 10S), dimeric (G2, 6.5S) and monomeric (G1, 4S) forms of AchE, but not the collagen-tailed A12(16S) form of the sympathetic ganglion. Three variants of these forms could be distinguished on the basis of their solubility properties: (i) secreted forms which do not interact with the detergent Triton X-100; (ii) cellular forms which may be solubilized in detergent-free buffer and which interact reversibly with Triton X-100; (iii) cellular forms which require detergent for solubility, and aggregate in its absence. By using a nonpenetrating inhibitor, we demonstrated that, in T28 stationary cells, the cellular G4 form is associated with the plasma membrane, whereas the G1 form is intracellular. During induction of AChE activity in T28 cells, the relative proportion of the G4 form increases, suggesting, in agreement with previous observations, that G1 is a metabolic precursor of G4. The evolution of AChE molecular forms released into the culture medium closely resembles that of the cellular forms. The preferential accumulation of the G4 molecules does not simply depend on the cellular level of G1. It is favoured by culture conditions which promote morphological differentiation, but does not require the actual extension of neurites. T28 cells as well as other neuroblastoma-derived cells appear to be useful experimental materials to investigate the regulatory mechanisms underlying the maturation of AChE globular forms.

The identity of the serotonin-sensitive aryl acylamidase with acetylcholinesterase from human erythrocytes, sheep basal ganglia and electric eel

The identity of the serotonin-sensitive aryl acylamidase with acetylcholinesterase from three diverse sources, namely sheep basal ganglia, human erythrocyte membrane and electric eel, was examined. Both the enzymes co-purified with constant ratios of specific activity from all the three sources by different affinity chromatographic techniques. The ratio of acetylcholinesterase to aryl acylamidase activity was highest for basal ganglia, less for erythrocyte and lowest for eel enzymes. Both the purified enzymes co-migrated on polyacrylamide gel electrophoresis either as a single species or multiple species under different conditions. Gel density gradient electrophoresis indicated identical migration rates of both the enzymes. Extraction of the enzymes from the three sources by different techniques of membrane disruption and subsequent gel filtration on Sepharose 6B showed multiple peaks of enzyme activity. Both the enzymes had identical elution profiles on Sepharose 6B gel filtration. All the enzyme peaks from Sepharose 6B on gel electrophoresis showed co-migration of the enzyme activities. Apart from inhibition by serotonin and acetylcholine the purified aryl acylamidases from all the three sources were potently inhibited by neostygmine, eserine and BW 284C51, all strong inhibitors of acetylcholinesterase. It is suggested that the serotonin-sensitive aryl acylamidase is identical with acetylcholinesterase.

Collagen-tailed and hydrophobic components of acetylcholinesterase in Torpedo marmorata electric organ

We have distinguished three fractions of acetylcholinesterase (AcChoE; acetylcholine acetylhydrolase, EC 3.1.1.7) from Torpedo marmorata electric organs, according to their solubilization characteristics. The low-salt-aggregating collagen-tailed forms are soluble in high-salt buffers; their hydrodynamic properties ae not modified in the presence of detergents. They constitute the A fraction, which amounts to about a third of the tissue's AcChoE activity. The low-salt-soluble (LSS) and detergent-soluble (DS) fractions are not sensitive to ionic strength and collagenase. In the presence of nonionic detergents or bile salts, both fractions behave as a monodisperse "6.3S" form, the properties of which have been investigated mostly in the case of Triton X-100. Disulfide bond reduction dissociates the detergent form into a smaller "5S" form. These two forms are thought to be, respectively, detergent-associated dimers and monomers. In the absence of detergent, the LSS fraction is polydisperse: it contains a major 8S component, 11S and 14S components, and faster-sedimenting aggregates, which appear to represent dimers, tetramers, and higher polymers. The heterogeneity of the 8S component in gel filtration suggests that it also contains variable noncatalytic elements. Upon removal of the detergent the DS fraction forms ill-defined aggregates. Trypsin induces quaternary rearrangements of part of the 8S component into 11S and 14S components, which are still convertible into the detergent form; therefore trypsin probably digests noncatalytic elements. Pronase and proteinase K, on the other hand, convert the enzyme into a dimeric form, G2, that does not interact with detergents, probably by cleaving a minor fragment of the subunit that is involved in hydrophobic interactions.

Differential behaviour of eel and erythrocyte acetylcholinesterase on N-methylacridine affinity columns. Importance of ligand affinity and concentration

The retention and elution of acetylcholinesterase from bovine erythrocytes and electric eel on N-methylacridinium affinity columns have been compared at various ligand concentrations. A soluble 7.7 S dimeric form of bovine erythrocyte acetylcholinesterase required a ligand concentration of 2.0-2.8 mumol/ml in 0.1 M NaCl for retention, compared to 0.44 mumol/ml for various forms of the electric eel acetylcholinesterase. The difference in the retention of acetylcholinesterase from these two sources could not be explained by differences in their oligomeric structure. The affinity of bovine erythrocyte acetylcholinesterase for N-methylacridinium was 13-fold or more lower than the electric eel acetylcholinesterase at similar ionic strengths. N-Methylacridinium appeared to react selectively with the catalytic anionic site of both enzymes. It was concluded that the affinity of the side arm ligand was the major determinant of the differences in the retention properties of the eel and erythrocyte acetylcholinesterase. The difference in affinity for N-methylacridinium probably reflects differences in the organic cation binding region of the two enzymes.