Lower Acetylcholinesterase Activity Research Articles

Substratum-induced modulation of acetylcholinesterase activity in cultured dorsal root ganglion neurons.

Acetylcholinesterase (AChE) has been shown to be transiently expressed in the developing nervous system during periods of neuronal migration and axonal outgrowth. We are investigating the possible interaction of substratum with AChE activity in dorsal root ganglion neurons (DRGN) cultured on substrata with varying degrees of permissiveness for neurite outgrowth: (1) extracellular matrix substrata: reconstituted basal lamina Matrigel (MGEL), laminin (LAM) and type I collagen (COL), and (2) organotypic substrata: unfixed, frozen sections of sciatic nerve (SN) and spinal cord (SC). In group 1, histochemical staining for AChE in DRGN was lowest on MGEL where outgrowth was most vigorous, intermediate on LAM, and highest on COL where neurite outgrowth was reduced by 55% compared to Matrigel and highly fasciculated. A similar trend was seen when the cultures were assayed biochemically, 2.84 +/- 0.14 nmoles ACh hydrolyzed/ganglion/hr (MGEL), 4.42 +/- 0.19 (LAM), 5.79 +/- 0.37 (COL). In group 2, SN supported an expansive outgrowth with lower AChE activity than in DRGN grown on SC where outgrowth was minimal. These studies show that the levels of AChE activity can be modulated by substratum, perhaps in proportion to the permissiveness of the substratum to neuritic outgrowth. These results are discussed in relation to possible non-cholinergic roles of AChE.

Influence of cetiedil on erythrocyte membrane microviscosity and acetylcholinesterase activity

Since one of the cellular targets of cetiedil, a vaso-erythroactive drug, is likely to be the erythrocyte membrane, we have studied the influence of this drug on erythrocyte membrane microviscosity and acetylcholinesterase activity. No effect was evidenced on microviscosity, as measured by fluorescence polarization of light emitted by DPH or TMA-DPH labelling of the lipid bilayer. Cetiedil, however, did lower acetylcholinesterase activity, but it did not directly inhibit this enzyme activity. It can therefore be considered as an amphiphilic drug that perturbs membrane properties without affecting the physical state of the erythrocyte membrane.

Effect of diisopropylfluorophosphate on muscarinic and gamma-aminobutyric acid receptors in visual cortex of cats

Administration of diisopropylfluorophosphate (DFP), an organophosphorus (OP) compound, irreversibly inhibits acetylcholinesterase (AChE) and results in cholinergic hyperactivity. This study investigated muscarinic and gamma-aminobutyric acid (GABA) receptor changes in visual cortex of cats following an acute exposure to DFP. A single acute administration of DFP (4 mg/kg) decreased the number of muscarinic receptors at 2, 10, and 20 hours after treatment. GABA receptors were elevated at 2 and 10 hours but returned to within control levels at 20 hours. No significant alteration in muscarinic or GABA receptor affinity was noted. In all cases cortical AChE activity was inhibited 60–90%. These findings show a down regulation of muscarinic receptors after DFP associated with low AChE activity. GABA receptors also are altered, and may be part of a compensatory mechanism to counteract excess cholinergic stimulation.

Delayed neuropathy and acute toxicity studies with pirimiphos-methyl in the hen

This paper describes studies aimed at determining the acute anticholinergic and delayed neurotoxic potential of the organophosphate insecticide pirimiphos-methyl (O-2-diethylamino-6-methylpyrimidin-4-yl O,O-dimethyl phosphorothioate) in the hen. Delayed neuropathy was assessed by biochemical measurement of neuropathy target esterase (NTE) activities in the brain and spinal cord, clinical signs of neuropathy over two 21-day periods and histological assessment of nervous tissue. Acetylcholinesterase (AChE) activity was also determined in the brain and spinal cord. Hens were given a single oral dose of 100 mg kg-1 pirimiphos-methyl, which was followed by a repeated dose after 21 days. Tri-o-cresyl phosphate (TOCP), 500 mg kg-1, was used as a positive control. All pirimiphos-methyl-treated hens received prophylactic doses of N-methylpyridinium-2-aldoxime methanesulphonate (P2S) and atropine sulphate. Hens dosed with pirimiphos-methyl had very low AChE activities (less than 20% of control) in both the brain and spinal cord, 24 and 48 h after dosing. In the TOCP-treated hens, the activities were about 90% of control. NTE activities in the brain and spinal cord of pirimiphos-methyl-treated hens were identical to those in the controls, while they were profoundly inhibited (greater than 80%) in the TOCP-treated hens. All hens dosed with pirimiphos-methyl showed the expected signs of AChE inhibition and, following recovery, usually by Day 5, no clinical signs of delayed neuropathy were seen. The TOCP-treated hens developed clinical signs of neuropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Lattices of high histochemical activity occur in the human, monkey, and cat superior colliculus

A lattice of high oxidative metabolic activity occurs in the intermediate gray layer of the human, monkey, and cat superior colliculus. It is composed of a matrix of high enzyme activity that surrounds pale islands or bands of lower activity. In the human the pale bands are 300–400μm wide while in the smaller colliculi of the monkey and cat they are 100–200μm wide. The lattice was demonstrated by studying either cytochrome oxidase or succinate dehydrogenase. In the cat and monkey the lattice occurs at the same depth as the lattice of intense acetylcholincsterase activity, but the two lattices are not in spatial register. In the human the lattice of high oxidative metabolic activity is in the middle of the intermediate gray layer, whereas the lattice of intensely stained cholinesterase activity is at the base of this layer, but again the two lattices are not in spatial register. However, in the middle of the intermediate gray layer of the human, there are elongated islands and bands of very low acetylcholinesterase activity that coincide with the pale islands and bands of low cytochrome oxidase activity. An additional lattice of high enzyme activity occurs based on the enzyme nicotinamide dinucleotide phosphate (reduced form)-diaphorase. This lattice is prominent in the cat, occurs more faintly in the monkey, but did not appear to be present in the human. In the intermediate gray layer it had a high degree of overlap with the acetylcholinesterase lattice. The lattice of high oxidative metabolism contains loosely knit clusters of large multipolar cells containing high cytochrome oxidase activity and these cells do not occur in the pale islands. By contrast the cell bodies in the intermediate gray layer that contain either acetylcholinesterase or the diaphorase occur both between and within the patches of corresponding, high enzyme activity. It is suggested that the acetylcholinesterase and diaphorase lattices are mainly associated with afferent fibers while the lattice of high oxidative metabolism is mainly associated with intrinsic cells. The lattices occur in all mammals studied to date and appear to represent a fundamental principle in the organization of the mammalian colliculus. It is concluded that the lattices will provide a useful basis for further studies of the relationship between the many afferent and efferent modules thought to exist in this structure.

Zonation in the rat cerebellar cortex: patches of high acetylcholinesterase activity in the granular layer are congruent with Purkinje cell compartments

The rat cerebellar cortex is built from parasagitally arranged modules with topographically ordered afferent and efferent projections. The intrinsic organization of the cerebellum is revealed by immunocytochemical staining with monoclonal antibody, mabQ113. In the cerebellum, mabQ113 recognizes a polypeptide epitope that is restricted to a subset of Purkinje cells. Antigenic Purkinje cells are clustered to form a complex pattern of parasagittal compartments. Several biochemical markers reveal a superficially similar organization of the cortex, and so it is important to determine how many independent maps are present. This report compares the mabQ113 antigen display to the patchy distribution of acetylcholinesterase (AChE). In the granular layer and the white matter of the adult cerebellar cortex there is a patchy AChE staining that includes both the hemispheres and the vermis. The staining is often not sharply resolved cytologically, but seems to be associated primarily with the synaptic glomeruli. The boundaries of these granular layer patches in the vermis correspond to the mabQ113 +/mabQ113 − boundaries of the overlying Purkinje cell compartments. Thus, AChE and mabQ113 antigen share a common compartmentation both in the vermis, and in the hemispheres. Both mabQ113 and AChE distributions develop postnatally in the cerebellar cortex. At birth (PO) there is neither AChE activity nor mabQ113 immunoreactivity. Both staining patterns emerge during the second postnatal week. In the vermis at P10, there is AChE activity in the granular layer and white matter, and the distribution is already patchy despite the absence of synaptic glomeruli. At the same age the mabQ113 immunoreactivity is found in all Purkinhe cells rather than a subset, and the band pattern has yet to mature. There is also transient AChE staining of Purkinje cell somata and dendrites. The AChE patches clarify between P10 and P20 along with the appearance of the synaptic glomeruli and the development of differential mabQ113 staining, but there is no reason to believe that the two are causally linked. In contrast to the cerebellar cortex. AChE staining in the cerebellar nuclei matures very early and at P0 the activity is already high. Zones of high and low AChE activity are seen in all the cerebellar nuclei and may be related to the distribution of the terminal fields of the different Purkinje cell populations. In conclusion, these data suggest that a common compartmentation of the cerebellar cortex is revealed by both mabQ113 and AChE, and thus that both granular and molecular layers are organized into congruent patches.

Nutrition and fetal brain maturation: II. Impact of maternal starvation on changing levels of acetylcholinesterase and enolase in vitro

The impact of maternal starvation during Days 17–20 of gestation was examined in 20-day fetal rat brain tissue cultured for 6 days in MEM and 10% adult rat serum. Acetylcholinesterase (AChE) activities were consistently greater in fetal brain cell cultures from starved mothers. When fetal tissues from starved mothers were continuously exposed to 72-h fasted serum, AChE activities increased from 1.03±0.14 to 1.59±0.21 μmol/h/mg protein ( P<0.001). In fetal tissues from fed mothers, lower AChE activities were increased from 0.78±0.09 to 1.04±0.07 μmol/h/mg protein ( P<0.05) when 72-h fasted serum was used to replace the fed serum during incubation. When fetal brain cell cultures from fed mothers were exposed for 6 days to graded concentrations of fed serum (2.5–15%), the activities of AChE fell reciprocally from 1.34±0.10 to 0.82±0.12 μmol/h/mg protein ( P<0.05). The levels of AChE activity in tissues exposed to fasted serum were consistently greater, but fell similarly from 1.62±0.10 to 0.97±14 μmol/h/mg protein ( P<0.01), when serum concentrations were increased from 2.5 to 15%. AChE activities were 30% higher in tissues incubated with cycloheximide 10 −3 M ( P<0.02). Unlike AChE, fetal brain enolase activities were unaffected by maternal starvation. In fetal brain cell cultures from fed mothers, enolase fell from 1.85±0.10 to 1.37±0.12 μmol/min/mg protein following exposure to fasted instead of fed serum ( P<0.02). In fetal cultures from starved mothers, enolase activities were depressed similarly from 1.76±0.08 to 1.41±0.09 μmol/min/mg protein when fasted replaced fed serum ( P<0.02). Thus, the fetal brain cell cultures appear to maintain enzymatic realignments imposed by maternal starvation for at least 6 days. In addition, serum from fasted animals has significant growth inhibiting properties manifested by heightened activities of AChE and lower activities of enolase.

Effect of insulin on murine megakaryocytopoiesis in a liquid culture system.

To examine the influence of insulin on megakaryocytopoiesis, we tested its effect on murine bone marrow cultures in a liquid culture system. In the presence of pokeweed mitogen-stimulated spleen cell conditioned medium in culture, insulin markedly enhanced megakaryocyte colony formation and increased the number and size of free megakaryocytes seen after 7 days. Many of the cells in cultures with insulin, however, were classified as immature, since they had a basophilic cytoplasm, a low cytoplasmic/nuclear ratio and low acetylcholinesterase activity. It is suggested that insulin potentiates murine marrow megakaryocytopoiesis in vitro, but that this is not accompanied by differentiation of the cells from the immature to mature state.

Extraocular muscles in the lamprey, Lampetra fluviatils L. II. Motor end plates

Motor innervation and particularly the structure of motor end plates (MEPs) was studied in the extraocular muscles of the lamprey, Lampetra fluviatilis L., by light and electron microscopy. Each muscle is supplied with numerous thin motor nerve fibres. Motor end plates are located at their ends or along their course. Two motor end plate types were distinguished: en grappe‐like plates with a low acetylcholinesterase (AChE) activity were observed on thin muscle fibres, whilst en plaque‐like plates with a high AChE activity were found on thick mitochondria‐rich and thick multifibrillar muscle fibres. The postsynaptic membrane of the former MEP type does not show the presence of infoldings, MEPs located on thick mitochondria‐rich fibres show occasional infoldings, whereas the postsynaptic membrane of MEPs present on thick multifibrillar fibres reveals numerous infoldings. Motor end plates present in the extraocular muscles in the lamprey possess features typical for higher vertebrates and elasmobranch fishes, as well as for Tunicata.

Whole Brain Acetylcholinesterase Activity in Lead-Exposed Japanese Quail

A study was conducted in which male and female Japanese quail were fed dietary lead as lead acetate from hatch through 12 weeks of age. Lead was added to the diet at 0, 1, 10, 100, and 1000 mg/kg feed. Significant reductions in whole brain acetylcholinesterase (AChE) activity were found at all treatment levels. Additionally, a sexual dimorphism in brain weight and AChE activity was found. Breeding males had heavier brain weights and lower AChE activity than females. Brain weight was not affected by lead treatment. However, females exhibited a greater lead-induced decrease in AChE activity.

Organophosphorus and carbamate resistance in the predacious miteTyphlodromus pyri due to insensitive acetylcholinesterase

The cause of parathion and propoxur resistance inTyphlodromus pyri was studied in a Dutch strain in which resistance was dependent on a semi-dominant gene. Activity of glutathione S-transferase and acetylcholinesterase and reaction rate of acetylcholinesterase with paraoxon and propoxur were measured in this resistant (R) and in a susceptible (S) strain. The R strain was 100-fold resistant to parathion and 2300-fold resistant to propoxur. A 36-fold reduction was found in rate of inhibition of acetylcholinesterase in the R strain for paraoxon, and a 14-fold reduction for propoxur. In combination with the monogenic nature of the resistance, this proves that the insensitivity of acetylcholinesterase is the cause of resistance. The rate constant of acetylcholinesterase inhibition at 25°C in the S and R strains was 1.5×105 and 4.2×103 M −1 min−1 respectively for paraoxon, and 5.1×104 and 3.6×103 M −1 min−1 for propoxur. There was no significant difference between the R and S strains in glutathione S-transferase activity. The R strain had a somewhat lower acetylcholinesterase activity than the S strain.

Correspondence between the Dopamine islands and striosomes of the mammalian striatum

During the development of the mammalian striatum, the early-forming dopamine innervation is broken up into macroscopic patches called “dopamine islands”. These express high tyrosine hydroxylase-like immunoreactivity and are also rich in acetylcholinesterase activity. The mature striatum has prominent macroscopic compartments called “striosomes” that were first characterized by their low acetylcholinesterase activity and since have been related to heterogeneities in striatal input-output organizations. This report describes two sets of experiments designed to determine the relationship between the dopamine islands and the striosomes. The distributions of striatal tyrosine hydroxylase-like immunoreactivity and acetylcholinesterase activity were first compared in a series of kittens and young cats ranging in age from 1–228 postnatal days. During this time, the pattern of tyrosine hydroxylase-like immunoreactivity changed from islandic (patchy) to diffuse, and the pattern of acetylcholinesterase staining changed from one of acetylcholinesterase-rich patches to one of acetylcholinesterase-poor striosomes. The dopamine islands were in register with the acetylcholinesterase-poor patches at early developmental stages and at later stages the islands matched striosomes. These observations establish a correspondence between the dopamine islands and striosomes and demonstrate that the acetylcholinesterase-rich patches of the immature caudate nucleus become the acetylcholinesterase-poor striosomes of the adult. In a second set of experiments, cat fetuses were exposed to [ 3H]thymidine at embryonic days 22–29 in order to label the clustered subpopulations of striatal neurons known from previous experiments to lie in striosomes [ Graybiel and Hickey (1982) Proc. natn. Acad. Sci. U.S.A. 79, 198–202]. The [ 3H]thymidine-labeled brains were examined at late fetal (embryonic days 50–52), early postnatal (days 1–21) and later postnatal (days 62–199) ages. The clusters of [ 3H]thymidine-labeled neurons were aligned with tyrosine hydroxylase-rich, acetylcholinesterase-rich patches early in development, and with acetylcholinesterase-poor striosomes at later stages. There were marked dorsoventral differences in the intensity of tyrosine hydroxylase-like immuno-reactivity in the dopamine islands and this was confirmed in neonatal rats. A “dorsal islandic system” was defined as having crisp, highly immunoreactive islands; ventrally, regions of low and medium tyrosine hydroxylase-like immunoreactivity formed a mosaic. These findings, taken together with previous work on the striosomes, suggests that heterogeneity in the arrangement of striatal efferents and neurotransmitter-related compounds, and in the disposition of other striatal afferents, may be related to the modular development of the dopamine-containing innervation of the striatum.

Inverse relationship between neurotensin receptors and neurotensin-like immunoreactivity in cat striatum.

The adult corpus striatum in mammals is divided into distinct histochemical compartments. If the cat caudate nucleus is stained for acetylcholinesterase a number of macroscopically visible zones appear that have lower acetylcholinesterase activity than the surrounding tissue. These patches, called 'striosomes', correspond to regions of high [Met]-enkephalin-like immunoreactivity and dense opiate receptor binding and are related to the uneven distribution of striatal efferent neurones and cortical afferent terminations. One of the highest concentrations of neurotensin-like immunoreactivity is in the striatum and the immunoreactive material co-elutes with synthetic neurotensin on gel chromatography. Recently, we have found that neurotensin-like immunoreactivity in the cat caudate nucleus coincides with the striosomes. We have now localized neurotensin receptors in the cat caudate nucleus by autoradiography and found low density in the neurotensin-rich striosomes and a high density in the neurotensin-poor surrounding tissue.

The distribution of hexokinase compared to cytochrome oxidase and acetylcholinesterase in the somatosensory cortex and the superior colliculus of the rat

The distribution of hexokinase, a general glycolytic enzyme, was compared to that of cytochrome oxidase and acetylcholinesterase (AChE) in the somatosensory cortex and the superior colliculus of the rat. The vibrissal barrel fields of the adult rat contain high hexokinase and cytochrome oxidase activity and low AChE activity. In the superior colliculus, hexokinase activity was highest in cell layers and discrete foci of intense activity were observed in the deep grey layer. This distribution was different from that of both cytochrome oxidase and AChE in this structure.

Asymmetric and globular forms of AChE in slow and fast muscles of 129/ReJ normal and dystrophic mice.

Acetylcholinesterase activities and molecular forms were studied in normal and dystrophic 129/ReJ mice, focusing on four predominantly fast-twitch muscles and the slow-twitch soleus. The asymmetric and globular forms were analyzed separately so that the effect of dystrophy on each form could be determined. This comparative study showed the following. (1) In the normal condition, each muscle exhibited a distinct distribution of the molecular forms. (2) The diversity among the fast muscles resulted mainly from variations in the proportions of the three globular forms; in contrast, these muscles showed a constant and precise A12/A8/A4 ratio. (3) The slow-twitch soleus clearly differed from the other muscles in its low acetylcholinesterase activity and distinct distribution of the molecular forms, characterized by a low level of G4 and a peculiar ratio among its asymmetric forms, resulting from a relative increase of the A8 and A4 forms. (4) In dystrophic mice, the diversity of the acetylcholinesterase distribution was lost; all the fast muscles displayed profiles exhibiting the characteristics typical of the soleus. The fast-twitch extensor digitorum longus, sternomastoid, and plantaris converged towards an identical set of acetylcholinesterase molecules. (5) In contrast, the acetylcholinesterase activity and molecular forms of the soleus were only slightly affected by the disease. These results reveal that the dystrophy modifies both categories of molecular forms of acetylcholinesterase in a very precise manner. Such complex changes, which are highly reproducible in a variety of different muscles, are unlikely to result from nonspecific reactions secondary to the disease.

Chemospecificity of ontogenetic units in the striatum: demonstration by combining [3H]thymidine neuronography and histochemical staining.

Neurons being generated in the striatum of 10 fetal cats were pulse labeled by injection of [3H]thymidine directly into the maternal uterus at times ranging between the 22nd and 30th days (E22-E30) of the 65-day gestational period. Many of the striatal neurons labeled during this interval were found, at adolescence, to form 100- to 600-mum-wide cell clusters in the caudate nucleus. In E24-E30 specimens, we compared the distributions of these cell clusters with the locations of patches of low acetylcholinesterase activity and high enkephalin immunoreactivity (the "striosomes') visualized in serially adjoining sections. We found precise matches between most of the cell clusters and the acetylcholinesterase-poor enkephalin-rich zones, regardless of the embryonic age at which exposure to the [3H]thymidine had occurred. We conclude that the histochemically distinct striosomal patch-works observed in the acetylcholinesterase and enkephalin preparations correspond to ontogenetic units of the striatum.

Detection of nicotinic cholinergic transmission in [formula omitted][formula omitted] electrop lax

Biochemical and electrophysiological studies were conducted on the electric organ of the electric fish of the Nile, Malapterurus electricus , in order to determine if transmission was chemically mediated. There was no binding of [ 3H] acetylcholine, [ 3H] quinuclidinyl benzilate or [ 3H]-perhydrohistrionicotoxin; but low acetylcholinesterase activity was observed, as was binding of [ 125I] α-bungarotoxin. The latter binding was detectable at 0.85 ± 0.07 pmol/g tissue, and was totally inhibited by 1 μM α-bungarotoxin or 100 μM d-tubocurarine. A tetrodotoxin-sensitive action potential was measured which was Na +- dependent. Depolarization (30–40 mV) was caused by carbamylcholine, and this was blocked by d-tubocurarine or α-bungarotoxin. The data suggest that this electric organ which may be a rich source for electrically excitable channels, is innervated by nicotonic cholinergic motoneurons, but the concentrations of acetylcholine receptors and acetylcholinesterase are very low.

An immunohistochemical study of enkephalins and other neuropeptides in the striatum of the cat with evidence that the opiate peptides are arranged to form mosaic patterns in register with the striosomal compartments visible by acetylcholinesterase staining

This report presents immunohistochemical evidence for a modular arrangement of enkephalin and substance P in the striatum of cats and kittens. In cross-sections from the adults, met-enkephalin immunoreactivity in the caudate nucleus was concentrated in discrete, variably shaped macroscopic patches (0.2–0.5 mm wide) spaced at roughly 0.7–1.0 mm intervals. Patches appeared only occasionally in the putamen but there were larger districts of high immunoreactivity in the nucleus accumbens. In sections incubated with antiserum to substance P, both patches of dense immunoreactivity and zones of low immunoreactivity were present in the caudate nucleus. Staining in the putamen was fairly homogeneous, while in the nucleus accumbens it was patterned and especially intense dorsally. A detailed comparison was made between the distribution of the enkephalin-rich patches and the circumscript zones of low acetylcholinesterase activity (striosomes) visible in serially-adjoining sections by the thiocholine method. There was a striking registration of the two sets of figures, nearly every cholinesterase-poor patch corresponding to an enkephalin-positive zone. Correspondences were more complicated in the substance P stain but many pale zones and some dark zones were aligned with the enkephalin-rich cholinesterase-poor figures. No comparable clumping of reaction product was visible in sections processed for somatostatin immunoreactivity. In the caudate nucleus of young kittens, small dark patches of enkephalin and substance P immunoreactivity also appeared. In the cholinesterase stain there were both light and dark patches, and it was mainly with the dark zones that the enkephalin-positive patches (and some substance P patches) were in register. We conclude that the caudate nucleus is divided up into pharmacologically distinct compartments, and that although these are present at birth, their final histochemical composition is established postnatally.

Reduced binding of ( 3H)-Quinuclidinyl benzilate associated with chronically low acetylcholinesterase activity

( 3H)-Quinuclidinyl benzilate (QNB) binding was examined in the cortex, striatum and hippocampus of rats repeatedly exposed to the anticholinesterase, diisopropyl fluorophosphate (DFP). Compared to vehicle-treated controls, a reduction in maximal binding of 25–30% was observed in these brain regions. The reduction in binding was associated with regional acetylcholinesterase (AChE) inhibition of 80–90%. A tendency of lower muscarinic acetylcholine receptor (m-AChR) affinity for ( 3H)-QNB in control preparations, compared to those from DFP-treated rats, was observed. However, only in the case of the striatal control homogenate was there a significant increase in apparent K D. A concomitant feature of chronically low AChE activity is therefore a reduction, mainly in number, of m-AChR's. These findings support the hypothesis that in the central nervous system (CNS) DFP tolerance and cholinomimetic subsensitivity may involve the m-AChR.

Relation between Low Erythrocyte Acetylcholinesterase Activity and Membrane Lipids in Paroxysmal Noctural Haemoglobinuria*

Acetylcholinesterase of intact erythrocytes, their ghost and salt soluble extracts obtained from patients with paroxysmal nocturnal haemoglobinuria (PNH) does not differ from normal with respect to Km values for acetylthiocholine, and Ki values for phenyltrimethylammonium iodide. However, the enzyme from PNH sources has lower V max values than normal, has different thermal stability from normal, has less distinctive transition temperature in the Arrhenius plots, and is less subject to inhibition by stearic acid. These results and that from comparison of activation of deoxycholate-extracted enzyme by lipids from normal erythrocytes suggest that the low acetylcholinesterase activity in PNH erythrocytes is due, at least in part, to alteration in the lipid environment of the enzyme.