Association of acetylcholinesterase with the cell surface

Choline acetyltransferase, acetylcholinesterase, and nicotinic acetylcholine receptors of human gingival and esophageal epithelia

A non-neuronal cholinergic system that includes neuronal-like nicotinic acetylcholine receptors (nAChRs) has recently been described in epithelial cells that line the skin and the upper respiratory tract. Since the use of nicotine-containing products is associated with morbidity in the upper digestive tract, and since nicotine may alter cellular functions directly via nAChRs, we sought to identify and characterize a non-neuronal cholinergic system in the gingival and esophageal epithelia. mRNA transcripts for alpha3, alpha5, alpha7, and beta2 nAChR subunits, choline acetyltransferase, and the asymmetric and globular forms of acetylcholinesterase were amplified from gingival keratinocytes (KC) by means of polymerase chain-reactions. These proteins were visualized in the gingival and esophageal epithelia by means of specific antibodies. Variations in distribution and intensity of immunostaining were found, indicating that the repertoire of cholinergic enzymes and receptors expressed by the cells changes during epithelial maturation, and that an upward concentration gradient of free acetylcholine exists. Blocking of the nAChRs with mecamylamine resulted in reversible loss of cell-to-cell adhesion, and shrinking and rounding of cultured gingival KC. Activation of the receptors with acetylcholine or carbachol caused stretching and peripheral ruffling of the cytoplasmic aprons, and formation of new intercellular contacts. These results demonstrate that both the keratinizing epithelium of attached gingiva and the non-keratinizing epithelium lining the upper two-thirds of the esophageal mucosa possess a non-neuronal cholinergic system. The nAChRs expressed by these epithelia are coupled to regulation of cell adhesion and motility, and may provide a target for the deleterious effects of nicotine.

Molecular modeling of the collagen-like tail of asymmetric acetylcholinesterase

The asymmetric form of acetylcholinesterase comprises three catalytic tetramers attached to ColQ, a collagen-like tail responsible for the anchorage of the enzyme to the synaptic basal lamina. ColQ is composed of an N-terminal domain which interacts with the catalytic subunits of the enzyme, a central collagen-like domain and a C-terminal globular domain. In particular, the collagen-like domain of ColQ contains two heparin-binding domains which interact with heparan sulfate proteoglycans in the basal lamina. A three-dimensional model of the collagen-like domain of the tail of asymmetric acetylcholinesterase was constructed. The model presents an undulated shape that results from the presence of a substitution and an insertion in the Gly-X-Y repeating pattern, as well as from low imino-acid regions. Moreover, this model permits the analysis of interactions between the heparin-binding domains of ColQ and heparin, and could also prove useful in the prediction of interaction domains with other putative basal lamina receptors.

Acetylcholinesterase of Schistosoma mansoni--functional correlates. Contributed in honor of Professor Hans Neurath's 90th birthday

Acetylcholinesterase (AChE) is an enzyme broadly distributed in many species, including parasites. It occurs in multiple molecular forms that differ in their quaternary structure and mode of anchoring to the cell surface. This review summarizes biochemical and immunological investigations carried out in our laboratories on AChE of the helmint, Schistosoma mansoni. AChE appears in S. mansoni in two principal molecular forms, both globular, with sedimentation coefficients of approximately 6.5 and 8 S. On the basis of their substrate specificity and sensitivity to inhibitors, both are "true" acetylcholinesterases. Approximately half of the AChE activity of S. mansoni is located on the outer surface of the parasite, attached to the tegumental membrane via a covalently attached glycosylphosphatidylinositol anchor. The remainder is located within the parasite, mainly associated with muscle tissue. Whereas the internal enzyme is most likely involved in termination of neurotransmission at cholinergic synapses, the role of the surface enzyme remains to be established; there are, however, indications that it is involved in signal transduction. The two forms of AChE differ in their heparin-binding properties, only the internal 8 S form of the AChE being retained on a heparin column. The two forms differ also in their immunological specificity, since they are selectively recognized by different monoclonal antibodies. Polyclonal antibodies raised against S. mansoni AChE purified by affinity chromatography are specific for the parasite AChE, reacting with both molecular forms, but do not recognize AChE from other species. They interact with the surface-localized enzyme on the intact organism, and produce almost total complement-dependent killing of the parasite. S. mansoni AChE is thus demonstrated to be a functional protein, involved in multifaceted activities, which can serve as a suitable candidate for diagnostic purposes, vaccine development, and drug design.

Peripheral binding site is involved in the neurotrophic activity of acetylcholinesterase

Acetylcholinesterase (AChE) catalyses the hydrolysis of the neurotransmitter acetylcholine and it has been implicated in several non-cholinergic actions, including neurite outgrowth and amyloid formation. We have studied the trophic function of brain AChE on neuronal cell metabolism and proliferation as well as the enzyme domain involved in such effects. Low AChE concentrations (0.1-2.5 nM) stimulated neurite outgrowth and induced cell proliferation as measured by MTT reduction and [3H]thymidine incorporation. The action of AChE was not affected by edrophonium and tacrine both active site inhibitors, but it was abolished by propidium and gallamine, two peripheral anionic binding site (PAS) ligands. We conclude that the PAS domain of AChE is involved in the neurotrophic activity of the enzyme.

Acetylcholinesterase in the neuromuscular junction

New findings regarding acetylcholinesterase (AChE) in the neuromuscular junction (NMJ), obtained in the last decade, are briefly reviewed. AChE is highly concentrated in the NMJs of vertebrates. Its location remains stable after denervation in mature rat muscles but not in early postnatal muscles. Agrin in the synaptic basal lamina is able to induce sarcolemmal differentiations accumulating AChE even in the absence of a nerve ending. Asymmetric A12 AChE form is the major molecular form of AChE in vertebrate NMJs. Extrajunctional suppression of this form is a developmental phenomenon. Motor nerve is able to reinduce expression of the A12 AChE form in the ectopic NMJs even in muscles with complete extrajunctional suppression of this form. The 'tail' of the A12 AChE form is made of collagen Q. It contains domains for binding AChE to basal lamina with ionic and covalent interactions. Muscle activity is required for normal AChE expression in muscles and its accumulation in the NMJs. In addition, the pattern of muscle activation also regulates AChE activity in the NMJs, demonstrating that the pattern of synaptic transmission is able to modulate one of the key synaptic components.

Stable complexes involving acetylcholinesterase and amyloid-beta peptide change the biochemical properties of the enzyme and increase the neurotoxicity of Alzheimer's fibrils

Brain acetylcholinesterase (AChE) forms stable complexes with amyloid-beta peptide (Abeta) during its assembly into filaments, in agreement with its colocalization with the Abeta deposits of Alzheimer's brain. The association of the enzyme with nascent Abeta aggregates occurs as early as after 30 min of incubation. Analysis of the catalytic activity of the AChE incorporated into these complexes shows an anomalous behavior reminiscent of the AChE associated with senile plaques, which includes a resistance to low pH, high substrate concentrations, and lower sensitivity to AChE inhibitors. Furthermore, the toxicity of the AChE-amyloid complexes is higher than that of the Abeta aggregates alone. Thus, in addition to its possible role as a heterogeneous nucleator during amyloid formation, AChE, by forming such stable complexes, may increase the neurotoxicity of Abeta fibrils and thus may determine the selective neuronal loss observed in Alzheimer's brain.

Acetylcholinesterase mRNA level and synaptic activity in rat muscles depend on nerve-induced pattern of muscle activation

Acetylcholinesterase (AChE) mRNA levels are severalfold higher in fast rat muscles compared with slow. We hypothesized that AChE mRNA levels and AChE activity in the neuromuscular junction depend on a specific nerve-induced pattern of motor unit activation. Chronic low-frequency stimulation, mimicking the activation pattern in slow muscles, was applied to fast muscles in rats. Molecular forms of AChE were analyzed by velocity sedimentation, and AChE mRNA levels were analyzed by Northern blots. AChE mRNA levels in stimulated fast muscles dropped to 10-20% of control after 1 week and became comparable to those in slow soleus muscles. The activity of the junctional A12 AChE form in 35 d stimulated fast muscles decreased to 56% of control value, reaching that in the soleus muscle. Therefore, synaptic AChE itself depends on the muscle activation pattern. Complete inactivity after denervation also decreased the AChE mRNA level in fast muscles to <10% in 48 hr. In contrast, profuse fibrillations observed in noninnervated immature regenerating muscles maintain AChE mRNA levels at 80% of that in the innervated fast muscles. If protein synthesis was inhibited by cycloheximide, AChE mRNA levels in 3-d-old regenerating muscle, still containing myoblasts, increased approximately twofold. No significant increase after cycloheximide application was observed either in denervated mature fast muscles or in normal slow muscles. Low AChE mRNA levels observed in those muscles are probably not caused by decreased stability of AChE mRNA as demonstrated in myoblasts.

A major portion of synaptic basal lamina acetylcholinesterase is detached by high salt- and heparin-containing buffers from rat diaphragm muscle and Torpedo electric organ

Collagen-tailed asymmetric acetylcholinesterase (AChE) forms are believed to be anchored to the synaptic basal lamina via electrostatic interactions involving proteoglycans. However, it was recently found that in avian and rat muscles, high ionic strength or polyanionic buffers could not detach AChE from cell-surface clusters and that these buffers solubilized intracellular non-junctional asymmetric AChE rather than synaptic forms of the enzyme. In the present study, asymmetric AChE forms were specifically solubilized by ionic buffers from synaptic basal lamina-enriched fractions, largely devoid of intracellular material, obtained from the electric organ of Torpedo californica and the end plate regions of rat diaphragm muscle. Furthermore, foci of AChE activity were seen to diminish in size, number, and staining intensity when the rat synaptic basal lamina-enriched preparations were treated with the extraction buffers. In the case of Torpedo, almost all the AChE activity was removed from the pure basal lamina sheets. We therefore conclude that a major portion of extracellular collagen-tailed AChE is extractable from rat and Torpedo synaptic basal lamina by high ionic strength and heparin buffers, although some non-extractable AChE activity remains associated with the junctional regions.

Brain acetylcholinesterase promotes amyloid-beta-peptide aggregation but does not hydrolyze amyloid precursor protein peptides

It has been suggested that acetylcholinesterase (AChE) has both a putative proteolytic activity against the amyloid precursor protein (APP), and a capacity to accelerate the assembly of amyloid-beta-peptide (Abeta) into Alzheimer's fibrils. Here, we have studied the ability of bovine brain AChE to share both activities. Results indicate that AChE purified through acridinium was able to process the APP peptides, however after further purification by an edrophonium column, the protease activity was lost. Under both conditions the capacity of the enzyme to promote amyloid formation was maintained. Kinetic studies of the Abeta aggregation process using edrophonium-AChE, indicated that the lag phase of the aggregation process was smaller than the one observed with the esterase purified by acridinium alone. Considering that the total amount of amyloid formed, measured by thioflavine-T fluorescence, was similar for both AChE preparations, our results suggest that the edrophonium-AChE possesses an higher intrinsic capacity to stimulate the aggregation of Abeta(1-40) peptide.

Non-classical actions of cholinesterases: role in cellular differentiation, tumorigenesis and Alzheimer's disease

The cholinesterases are members of the serine hydrolase family, which utilize a serine residue at the active site. Acetylcholinesterase (AChE) is distinguished from butyrylcholinesterase (BChE) by its greater specificity for hydrolysing acetylcholine. The function of AChE at cholinergic synapses is to terminate cholinergic neurotransmission. However, AChE is expressed in tissues that are not directly innervated by cholinergic nerves. AChE and BChE are found in several types of haematopoietic cells. Transient expression of AChE in the brain during embryogenesis suggests that AChE may function in the regulation of neurite outgrowth. Overexpression of cholinesterases has also been correlated with tumorigenesis and abnormal megakaryocytopoiesis. Acetylcholine has been shown to influence cell proliferation and neurite outgrowth through nicotinic and muscarinic receptor-mediated mechanisms and thus, that the expression of AChE and BChE at non-synaptic sites may be associated with a cholinergic function. However, structural homologies between cholinesterases and adhesion proteins indicate that cholinesterases could also function as cell-cell or cell-substrate adhesion molecules. Abnormal expression of AChE and BChE has been detected around the amyloid plaques and neurofibrillary tangles in the brains of patients with Alzheimer's disease. The function of the cholinesterases in these regions of the Alzheimer brain is unknown, but this function is probably unrelated to cholinergic neurotransmission. The presence of abnormal cholinesterase expression in the Alzheimer brain has implications for the pathogenesis of Alzheimer's disease and for therapeutic strategies using cholinesterase inhibitors.

Acetylcholinesterase accelerates assembly of amyloid-beta-peptides into Alzheimer's fibrils: possible role of the peripheral site of the enzyme

Acetylcholinesterase (AChE), an important component of cholinergic synapses, colocalizes with amyloid-beta peptide (A beta) deposits of Alzheimer's brain. We report here that bovine brain AChE, as well as the human and mouse recombinant enzyme, accelerates amyloid formation from wild-type A beta and a mutant A beta peptide, which alone produces few amyloid-like fibrils. The action of AChE was independent of the subunit array of the enzyme, was not affected by edrophonium, an active site inhibitor, but it was affected by propidium, a peripheral anionic binding site ligand. Butyrylcholinesterase, an enzyme that lacks the peripheral site, did not affect amyloid formation. Furthermore, AChE is a potent amyloid-promoting factor when compared with other A beta-associated proteins. Thus, in addition to its role in cholinergic synapses, AChE may function by accelerating A beta formation and could play a role during amyloid deposition in Alzheimer's brain.

Molecular forms of tegumental and muscle acetylcholinesterases of Schistosoma

Acetylcholinesterase (AChE) is present in the muscle and on the tegument of schistosomes. Molecular forms of schistosome AChE were examined because particular AChEs are found in tissues of distinct function elsewhere. The dimeric globular form (G2) is the only form evident in adult Schistosoma haematobium: 32% of the muscle AChE is hydrophilic and 61% is membrane associated. A substantial amount of this enzyme is phosphatidylinositol (PI) anchored since it could be released by PI-specific phospholipase C from both muscle and tegumental membranes.

Effect of protamine on the solubilization of collagen-tailed acetylcholinesterase: potential heparin-binding consensus sequences in the tail of the enzyme

Asymmetric acetylcholinesterase (AChE) contains three tetrameric sets of catalytic subunits disulfide-linked to structural subunits of a collagenic tail. This form is localized in the basement membrane zone of the neuromuscular junction, where it interacts with proteoglycans. It has been described that heparin-binding domains of many proteins contains clusters of basic residues. Here we show that protamine--a highly basic protein--specifically solubilizes asymmetric AChE from the rat neuromuscular junction, starting at 25 micrograms/ml and reaching a plateau at 250 micrograms/ml protamine. We also show that protamine was able to displace AChE bound to heparin-agarose. Two synthetic peptides corresponding to the sequence of the collagenic tail polypeptide also release the enzyme. Finally, we propose that two heparin-binding consensus sequences (-B-B-X-B-) are present in the tail of AChE. Our results indicate that clusters of basic residues are responsible for the interaction of the collagen-tailed AChE with proteoglycans.

Two heparin-binding domains are present on the collagenic tail of asymmetric acetylcholinesterase

The collagen-tailed form of acetylcholinesterase (AChE) binds to heparin and heparan sulfate proteoglycans. We have employed synthetic peptides corresponding to the central collagenic region of the tail of AChE, to identify the heparin-binding domains of the tail of asymmetric AChE. Two putative heparin-binding consensus sequences were localized in the collagenic tail. Peptides containing such sequences (P-(145-159) and P-(249-262)) were able to release asymmetric AChE bound to heparin-agarose. A triple mutation, Asn-Asp-Gly-Gly instead of Arg-His-Gly-Arg, completely abolishes the capacity of the peptide P-(145-159) to elute AChE from the heparin column. Our results suggest that the interaction between the collagen-tailed AChE and proteoglycans is mediated by clusters of basic residues that form two belts around the triple helix of the collagenic tail.

Sensitivity of acetylcholinesterase molecular forms to inhibition by high MgCl2 concentration

Previous studies have shown that the asymmetric (A12) and the dimeric (G2), but not the tetrameric (G4), acetylcholinesterase (AChE) forms are inactivated by high MgCl2 concentration (Perelman and Inestrosa (1989) Anal. Biochem. 180, 227-230). Here we show that the effect of MgCl2 on AChE activity corresponds to an irreversible inhibition and is not due to environmental effects related to the different extraction media. The anchor domain in each AChE form was not involved in the differential MgCl2 sensitivity. Monomers derived from the various AChE forms behave in a way similar to that of the original assembled forms. Purified AChE molecular forms showed the same sensitivity to MgCl2, than the same enzyme forms studied in tissue extracts. Neither the affinity for the substrate nor the inhibition by excess substrate of the residual AChE activity were affected by high MgCl2 concentration. Results indicate that the differences between the tetrameric enzyme and the other two AChE molecular forms occur at the level of the catalytic subunit, probably due to differential post-translational processing.

Monomeric amphiphilic forms of acetylcholinesterase appear early during brain development and may correspond to biosynthetic precursors of the amphiphilic G4 forms

We have studied the development of mouse brain acetylcholinesterase (AChE). Only tetrameric (G4) and monomeric (G1) forms were detected both in vivo and in vitro. The amphiphilic G4 form increased continuously during development, whereas an amphiphilic G1 form appears transiently around embryonic day 17. A causal relationship between the monomers and tetramers was established using pulse-chase experiments with paraoxon, a reversible AChE inhibitor. We report here, for the first time, the presence of an amphiphilic monomer possibly involved in the assembly of the amphiphilic G4 AChE form during mouse brain development.

Blood markers in Alzheimer disease: subnormal acetylcholinesterase and butyrylcholinesterase in lymphocytes and erythrocytes

In patients with the clinical diagnosis of Alzheimer disease (AD), we searched for systemic changes in components of the blood as a diagnostic tool. The acetylcholine-related enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) were measured in plasma, erythrocytes, platelets and lymphocytes. Results did not show a general effect; notwithstanding, specific cell types presented alterations either in AChE or BuChE but not in both enzymatic activities. In AD patients, AChE of lymphocytes was reduced by 60% compared with the age-matched controls. However, when patients were divided, the sporadic but not the familial subgroup exhibited a significant reduction. In erythrocytes the BuChE activity was reduced by 45% in sporadic AD. The molecular forms of the lymphocyte AChE were characterized by velocity sedimentation. Both globular forms were subnormal, more so the tetrameric G4 AChE form than the G2 form.

Monoclonal antibodies against brain acetylcholinesterases which recognize the subunits bearing the hydrophobic anchor

Monoclonal antibodies were raised against amphiphilic detergent-soluble (DS) acetylcholinesterase (AChE) from human brain caudate nucleus. Three mAb, 132-4 (IgG1), 132-5 (IgG1) and 132-6 (IgG3), specific for brain DS-AChE were selected and subcloned. These mAb reacted with native as well as heat-denatured and SDS-denatured DS-AChE, indicating that the epitopes to which mAb bound are continuous determinants. The mAb cross-reacted with DS-AChE from bovine and mouse brain and with brain DS-AChE from river trout (Salmo trutta forma fario) and lake trout (Salmo trutta forma lacustris). No cross-reaction was detected with the following antigens: salt-soluble (SS) AChE from bovine brain, glycophospholipid-anchored AChE from human and bovine erythrocytes, DS-butyrylcholinesterase and SS-butyrylcholinesterase (BtChE) from the brains of human and bovine, DS-BtChE from chicken and BtChE from human serum. Deglycosylation of brain DS-AChE with N-glycosidase F did not abolish the binding of mAb to DS-AChE. After reduction of brain DS-AChE by dithiothreitol, the mAb no longer reacted with the antigen, indicating that a disulfide bridge is important for the epitope. Monomerization of brain DS-AChE by trypsin and limited proteinase K treatment also abolished the binding of mAb to DS-AChE. Sucrose-density-gradient centrifugation showed that mAb reacted only with native tetrameric forms, but not with dimeric and monomeric forms. Western blot, after SDS/PAGE under non-reducing conditions, showed that mAb reacted with those subunits carrying the hydrophobic anchor (i.e. tetramers, trimers and heavy dimers) but not with those devoid of it (light dimers or monomers). Since mAb 132-4, 132-5 and 132-6 recognized DS-AChE from fish up to mammalian brain in the evolutionary tree, it is concluded that the epitope to which these mAb bind, is conserved in nature.

Human keratinocytes synthesize, secrete, and degrade acetylcholine

We previously reported that normal human keratinocytes express muscarinic receptors, and that acetylcholine induces attachment of these cells to each other. We have now studied the ability of human keratinocytes to synthesize, secrete, and degrade acetylcholine. To detect and localize the synthesizing enzyme choline acetyltransferase and degrading enzyme acetylcholinesterase, cultured cells and cryostat sections of normal human skin were pre-incubated with specific monoclonal antibodies and stained with an avidin-biotin complex/alkaline phosphatase. The choline acetyltransferase activity was assessed by the conversion of [3H]acetyl CoA to [3H]acetylcholine, and newly synthesized [3H]acetylcholine was detected using thin-layer chromatography. The acetylcholinesterase activity was measured spectrophotometrically. Both cholinergic enzymes were present in cultured keratinocytes, and in basal, spinous and granular epidermal cell layers. Choline acetyltransferase was visualized in the vicinity of cell nuclei, and acetylcholinesterase was observed in or near cell membranes. Newly synthesized acetylcholine was detected in both cell homogenates and culture supernatants. The estimated Vmax of the synthesis of labeled acetylcholine by homogenized keratinocytes was about 20 pmoles acetylcholine produced/mg protein/min at 37 degrees C. A single keratinocyte synthesized a mean of 2 x 10(-17) moles, and released 7 x 10(-19) moles acetylcholine per minute. Both cell homogenates and culture supernatants exhibited similar acetylcholinesterase activities indicating that human keratinocytes secrete acetylcholinesterase, too. Thus, we have demonstrated that normal human keratinocytes possess choline acetyltransferase and acetylcholinesterase, and synthesize, store, release, and degrade acetylcholine. Because human keratinocytes can also respond to acetylcholine, we believe that keratinocyte acetylcholine works in the epidermis as a local hormone.

External GTP alters the motility and elicits an oscillating membrane depolarization in Paramecium tetraurelia

Paramecium, a unicellular ciliated protist, alters its motility in response to various stimuli. Externally added GTP transiently induced alternating forward and backward swimming interspersed with whirling at a concentration as low as 0.1 microM. ATP was 1000-fold less active, whereas CTP and UTP produced essentially no response. The response to the nonhydrolyzable GTP analogs guanosine 5'-[gamma-thio]triphosphate and guanosine 5'-[beta, gamma-imido]triphosphate was indistinguishable from that to GTP. This behavioral response was correlated with an unusual transient and oscillating membrane depolarization in both wild-type cells and the mutant pawn B, which is defective in the voltage-dependent Ca2+ current required for action potentials. This is a specific effect of external GTP on the excitability of a eukaryotic cell and, to our knowledge, is the first purinergic effect to be discovered in a microorganism.

Decorin is specifically solubilized by heparin from the extracellular matrix of rat skeletal muscles

We have previously communicated that heparin co-solubilizes the asymmetric form of acetylcholinesterase (AChE) and a dermatan sulfate proteoglycan from the extracellular matrix (ECM) of rat skeletal muscles. In this report we unequivocally demonstrate by biochemical and immunological analyses that the proteoglycan that is solubilized by heparin from rat skeletal muscle ECM corresponds to decorin. These results support the concept for the role of decorin in the ECM organization.

Amphiphilic behavior of a brain tetrameric acetylcholinesterase form lacking the plasma membrane anchoring domain

We have studied the behavior of a mammalian brain tetrameric acetylcholinesterase (AChE) form released by proteinase K from a crude membrane fraction of bovine caudate nucleus. The solubilization of active AChE indicated the presence of a protease-sensitive site in the anchored protein. Unexpectedly, the solubilized AChE maintained its capacity to form aggregates in detergent-free gradients. We demonstrate here that this property was due neither to the presence of the hydrophobic membrane-anchoring domain still linked to the enzyme, nor to the presence of AChE activity trapped in small plasma membrane vesicles. Moreover, we found that the proteinase K-treated extract, devoid of AChE activity, induced the aggregation of purified hydrophilic AChE which usually does not form aggregates. Our results suggest the presence of an AChE aggregating factor in bovine brain extracts prepared in the presence of proteinase K. It is possible that this aggregation may reflect a process of AChE clustering on neurons.

Monomerization of tetrameric bovine caudate nucleus acetylcholinesterase. Implications for hydrophobic assembly and membrane anchor attachment site

Tetrameric detergent-soluble bovine caudate nucleus acetylcholinesterase (AChE) was reduced and alkylated under conditions in which at least 95% of initial activity is retained. This treatment alone did not result in monomerization of AChE, nor did it create a hydrophilic enzyme. However, in the presence of SDS the enzyme became monomerized. Incubation of AChE with trypsin in the presence of the reversible inhibitor edrophonium rendered the enzyme hydrophilic and led to catalytically active monomers being produced. SDS/PAGE of this preparation in non-reducing conditions revealed only a small decrease in the subunit molecular mass. N-Terminal sequencing of the enzyme, before and after trypsin treatment, yielded identical N-termini showing that the enzyme was monomerized subsequent to C-terminal tryptic cleavage. From our results, we conclude that the most C-terminal cysteine residue is involved in inter-subunit disulphide bonding as well as in the attachment of AChE to the membrane anchor. Furthermore, the C-terminal region in the primary structure provides an area for hydrophobic contacts between the different subunits and also between the subunits and the membrane anchor.

Genetic analysis of proteoglycan structure, function and metabolism

Significant progress has been made in understanding the structure, function, and metabolism of proteoglycans. Many of the advances derive from the application of recombinant DNA methodology to their core proteins and from the characterization of animal cell mutants altered in glycosaminoglycan synthesis.

Chondroitinases release acetylcholinesterase from chick skeletal muscle

Bacterial chondroitinases (both ABC and AC types) release asymmetric and globular forms of AChE from chick skeletal muscle samples. Heparinases, however, including heparitinase I, fail to do so under different incubation conditions. These results do not support the direct implication of the heparin/heparan sulfate family of GAGs in the interaction of the different AChE molecular forms with the muscle ECM. GAGs of the chondroitin/dermatan sulfate group could however be involved, either directly or indirectly, in the attachment of the AChE collagen-like tail to the muscle basal lamina.

A comparison of the Xenopus laevis oocyte acetylcholinesterase with the muscle and brain enzyme suggests variations at the post-translational level

1. Xenopus laevis oocytes express endogenously two components of the cholinergic system: the muscarinic receptors and the acetylcholinesterase (AChE). 2. A biochemical characterization of this enzyme was carried out. 3. The results established that the activity found in the oocytes correspond to 'true' AChE with a molecular weight of 65,000 Da and a sedimentation coefficient of 3-4 S. 4. The enzyme aggregates in the absence of detergent suggesting that it possess an hydrophobic character; despite that, it is not sensitive to PIPLC. 5. A comparison with the Xenopus brain and muscle AChE shows different post-translational modifications and catalytic properties with the oocyte AChE.