G4 forms of acetylcholinesterase and butyrylcholinesterase in normal and dystrophic mouse muscle differ in their interaction with Ricinus communis agglutinin

Differences in glycosylation between molecular forms of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in muscle and serum of normal and dystrophic mice have been studied by means of their adsorption to immobilized lectins. Application of a two-step extraction procedure, first with saline buffer, and second with saline buffer and Triton X-100, brought into solution most of the muscle AChE and BuChE activities. The AChE activity was five times greater than that of BuChE in normal (NM) and dystrophic muscle (DM). The AChE activity in the serum of dystrophic mice was twice that measured in control animals, but the BuChE activity remained almost unchanged. Both AChE and BuChE in muscle and serum bound completely to concanavalin A (Con A) and Lens culinaris agglutinin (LCA). A12, A8 and G4 AChE, but not the light G2 and G1 AChE forms, in NM and DM were completely adsorbed to wheat germ agglutinin (WGA). Similarly, G4 BuChE, but not the G2 and G1 forms, were associated to WGA. A high proportion of G4 and G1 AChE and G4 BuChE forms in mouse serum were fixed to WGA. Asymmetric AChE in NM and DM reacted with Ricinus communis agglutinin (RCA) but the light AChE and BuChE forms in muscle and serum did not bind to the lectin. G4 AChE and G4 BuChE in NM were not recognized by RCA, but the isoforms in DM bound fully to the lectin. Serum G4 AChE from control or dystrophic mice did not react with RCA, but G4 BuChE was fixed to the lectin. Since RCA is specific for galactose, the results suggest that in dystrophic muscle galactose is incorporated early in G4 AChE and this affects the level of the functional tetramers destined for insertion in the plasma membrane.

Human butyrylcholinesterase as a general prophylactic antidote for nerve agent toxicity. In vitro and in vivo quantitative characterization

Butyrylcholinesterase purified from human plasma (HuBChE) was evaluated both in vitro and in vivo in mice and rats as a single prophylactic antidote against the lethal effects of highly toxic organophosphates (OP). The variation among the bimolecular rate constants for the inhibition of HuBChE by tabun, VX, sarin, and soman was 10-fold (0.47 to 5.12 x 10(7) M-1 min-1; pH 8.0, 26 degrees). The half-life of HuBChE in blood after its i.v. administration in mice and rats was 21 and 46 hr, respectively. The peak blood-enzyme level was obtained in both species approximately 9-13 hr following i.m. injection of HuBChE, and the fraction of the enzyme activity absorbed into the blood was 0.9 and 0.54 for rats and mice, respectively. The stoichiometry of the in vivo sequestration of the anti-cholinesterase toxicants was consistent with the HuBChE/OP ratio of the molar concentration required to inhibit 100% enzyme activity in vitro. Linear correlation was demonstrated between the blood level of HuBChE and the extent of protection conferred against the toxicity of nerve agents. Pretreatment with HuBChE alone was sufficient not only to increase survivability following exposure to multiple median lethal doses of a wide range of potent OPs, but also to alleviate manifestation of toxic symptoms in mice and rats without the need for additional post-exposure therapy. It appeared that in order to confer protection against lethality nerve agents had to be scavenged to a level below their median lethal dose LD50 within less than one blood circulation time. Since the high rate of sequestration of nerve agents by HuBChE is expected to underlie the activity of the scavenger in other species as well, a reliable extrapolation of its efficacy from experimental animals to humans can be made.

Wuchereria bancrofti: identification of parasitic acetylcholinesterase in microfilariae infected human serum

An antigen with cholinesterase activity was detected in the sera of patients infected with Wuchereria bancrofti. The asymptomatic microfilaremic sera showed 3 to 4 times more cholinesterase activity for acetylthiocholine (ATCh) as compared to sera of symptomatic amicrofilaremic, hookworm infected and endemic normals, whereas the activities for butyrylthiocholine (BTCh) did not significantly differ. The enzyme activities from both sources, namely from sera of microfilaremic cases and from endemic normals, were partially purified and according to substrate specificity for ATCh and BTCh as well as inhibition of the former activity by excess substrate classified as acetylcholinesterase (AChE; EC 3.1.1.7) and pseudocholinesterase (AChE; EC 3.1.1.8), respectively. The Km-value for ATCh of the cholinesterase from the microfilaremic sera was determined to be 0.87 mM. Eserine competitively inhibited the AChE activity; the inhibition constant was found to be 1.3 microM. The BChE from the normal sera had Km-values of 0.15 and 0.20 mM for BTCh and ATCh, respectively, and did not show significant inhibition by eserine. These and other dissimilarities suggest a difference in nature of the cholinesterases in microfilaremic and normal sera and propose that the former enzyme, a true acetylcholinesterase, originates from the parasite. Additional evidence for the origin of the AChE-activity from the parasite was provided by ELISA-studies; anti-Brugia malayi AChE antibodies confirmed antigenecity and cross reactivity of the AChE in infected sera, whereas the antibodies did not show any cross reactivity with the BChE in normal sera.

Sheep brain pseudocholinesterase: inhibition kinetics of the partially purified enzyme by some substrate analogues

Pseudocholinesterase (ChE) (acylcholineacylhydrolase, EC 3.1.1.8) has been partially purified (about 270-fold) from sheep brain. The procedure included ammonium sulfate fractionation (20-80%), DEAE-Trisacryl M chromatography and procainamide-Sepharose 4B affinity chromatography. The molecular weight of purified ChE was found to be 290,000 by gel filtration. Kinetic properties of the enzyme have been studied using the substrate analogues choline, succinylcholine and benzoylcholine. It was shown that the inhibition was partially competitive.

Purification and immunological characterization of pigeon serum butyrylcholinesterase. Implications on environmental monitoring and toxicological testing of birds

Butyrylcholinesterase (EC 3.1.1.8) (BChE) was purified from pigeon serum to electrophoretic homogeneity by a four-step procedure involving blue sepharose CL-6B chromatography, ion exchange chromatography, procainamide affinity chromatography and gel filtration. An overall 2789-fold purification was achieved, with a final specific activity of 61.35 mumol/min/mg. The purified enzyme separated into two peaks when filtered through a column of Sephacryl S-300, a smaller peak containing the tetrameric form of BChE (C4) and a larger peak containing the monomeric form of BChE (C1). Native polyacrylamide gel electrophoresis (PAGE) of both peaks revealed single protein bands which coincided with esterase activity, with approximate M(r) values of 84,000 and 340,000, respectively. The C1 monomer represented 85-90% of the activity found in the pigeon serum. It is not clear whether this polymorphism of BChE in vertebrates contributes to the wider inter-individual variations observed in xenobiotics elimination kinetics and in the response to the pharmacological and toxic effects of pesticides. PAGE of the monomeric form of the enzyme in the presence of sodium dodecyl sulphate showed only one protein band with a M(r) of 84,000, while that of the tetrameric form revealed two bands, a major protein band (84,000) and a minor band (170,000), representing the monomer and the dimer of the dissociated tetrameric BChE enzyme under reducing conditions. Highly specific polyclonal antibodies were raised in rabbits against the purified enzyme. These antibodies cross-reacted with other avian BChEs, a criterion which make them useful for the immunopurification of other BChEs from different species as well as for biomonitoring and toxicological studies on the role of esterases as an indicator of avian exposure to organophosphorous pesticides.

Changes in acetylcholinesterase and butyrylcholinesterase in Alzheimer's disease resemble embryonic development--a study of molecular forms

The pattern of molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BChE, EC 3.1.1.8) separated by density gradient centrifugation was investigated in the brain and cerebrospinal fluid in Alzheimer's disease (AD), in human embryonic brain and in rat brain after experimental cholinergic deafferentation of the cerebral cortex. While a selective loss of the AChE G4 form was a rather constant finding in AD, a small but significant increase of G1 for both AChE and BChE was found in the most severely affected cases. Both in normal human brain and in AD a significant relationship could be established between the AChE G4/G1 ratio in different brain regions and the activity of choline acetyltransferase (ChAT). A similar decrease of the AChE G4 form as observed in AD can be induced in rat by experimental cholinergic deafferentation of the cerebral cortex. The increase in G1 of both AChE and BChE in different brain regions in AD is quantitatively related to the local density of neuritic plaques which are histochemically reactive for both enzymes. In human embryonic brain, a high abundance of G1 and a low G4/G1 ratio for both AChE and BChE was found resembling the pattern observed in AD. Furthermore, both in embryonic brain and in AD AChE shows no substrate inhibition which is a constant feature of the enzyme in the adult human brain. It is, therefore, concluded that the degeneration of the cholinergic cortical afferentation in AD as reflected by a decrease of AChE G4 is accompanied by the process of a neuritic sprouting response involved in plaque formation which is probably associated with the expression of a developmental form of the enzyme.

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.

Intramolecular relationships in cholinesterases revealed by oocyte expression of site-directed and natural variants of human BCHE

Structure-function relationships of cholinesterases (CHEs) were studied by expressing site-directed and naturally occurring mutants of human butyrylcholinesterase (BCHE) in microinjected Xenopus oocytes. Site-directed mutagenesis of the conserved electronegative Glu441,Ile442,Glu443 domain to Gly441,Ile442,Gln443 drastically reduced the rate of butyrylthiocholine (BTCh) hydrolysis and caused pronounced resistance to dibucaine binding. These findings implicate the charged Glu441,Ile442,Glu443 domain as necessary for a functional CHE catalytic triad as well as for binding quinoline derivatives. Asp70 to Gly substitution characteristic of 'atypical' BCHE, failed to alter its Km towards BTCh or dibucaine binding but reduced hydrolytic activity to 25% of control. Normal hydrolytic activity was restored to Gly70 BCHE by additional His114 or Tyr561 mutations, both of which co-appear with Gly70 in natural BCHE variants, which implies a likely selection advantage for these double BCHE mutants over the single Gly70 BCHE variant. Gly70 BCHE variants also displayed lower binding as compared with Asp70 BCHE to cholinergic drugs, certain choline esters and solanidine. These effects were ameliorated in part by additional mutations or in binding solanidine complexed with sugar residues. These observations indicate that structural interactions exist between N' and C' terminal domains in CHEs which contribute to substrate and inhibitor binding and suggest a crucial involvement of both electrostatic and hydrophobic domains in the build-up of the CHE active center.

Cholinesterases exhibiting aryl acylamidase activity in human amniotic fluid

Acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8) in human amniotic fluid were estimated in the presence of selective inhibitors. Amniotic fluid cholinesterases (mixture of acetylcholinesterase and butyrylcholinesterase) purified by procainamide-Sepharose affinity chromatography exhibited aryl acylamidase activity which was sensitive to serotonin inhibition (a property of aryl acylamidases associated with both acetyl- and butyrylcholinesterases) and tyramine activation (shown exclusively by aryl acylamidase associated with butyrylcholinesterase). Tyramine activation was unaffected in the presence of the selective acetylcholinesterase inhibitor BW284C51 whereas it was abolished in the presence of the selective butyrylcholinesterase inhibitor ethopropazine, suggesting the presence of both types of aryl acylamidases in amniotic fluid, one associated with acetylcholinesterase and the other associated with butyrylcholinesterase. Butyrylcholinesterase and the associated aryl acylamidase activity in the affinity purified enzyme was selectively immunoprecipitated by a polyclonal antibody raised against human serum butyrylcholinesterase. Estimation of the activity ratio of acetylcholinesterase to butyrylcholinesterase in a few samples of amniotic fluid showed that this could vary depending on the butyrylcholinesterase arising from contaminating blood in the samples. Gel electrophoresis under non-denaturing conditions and enzyme staining showed that butyrylcholinesterase band was detectable on the gel in all the samples whereas acetylcholinesterase band was below detectable levels in normal samples but visible in samples from pregnancies of neural tube defect fetuses. It is suggested that the use of selective cholinesterase inhibitors along with gel electrophoresis and immunoprecipitation studies may be useful in the assessment of cholinesterase activities in human amniotic fluid.

A comparative Raman spectroscopic study of cholinesterases

We report Raman spectra of various cholinesterases: lytic tetrameric forms (G4) obtained by tryptic digestion of asymmetric acetylcholinesterase (AChE) from Torpedo californica and Electrophorus electricus, a PI-PLC-treated dimeric form (G2) of AChE from T marmorata, and the soluble tetrameric form (G4) of butyrylcholinesterase (BuChE) from human plasma. The contribution of different types of secondary structure was estimated by analyzing the amide I band, using the method of Williams. The spectra of cholinesterases in 10 mM Tris-HCl (pH 7.0) indicate the presence of both alpha-helices (about 50%) and beta-sheets (about 25%), together with 15% turns and 10% undefined structures. In 20 mM phosphate buffer (pH 7.0), the spectra indicated a smaller contribution of alpha-helical structure (about 35%) and an increased beta-sheet content (from 25 to 35%). This shows that the ionic milieu profoundly affects either the conformation of the protein (AChE activity is known to be sensitive to ionic strength), or the evaluation of secondary structure, or both. In addition, we analyzed vibrations corresponding to the side chains of aromatic and aliphatic amino acids. In particular, the analyses of the tyrosine doublet (830-850 cm-1) and of the tryptophan vibration at 880 cm-1 indicated that these residues are predominantly 'exposed' on the surface of the molecules.

Localization of the peptidase activity of human serum butyrylcholinesterase in a approximately 50-kDa fragment obtained by limited alpha-chymotrypsin digestion

Purified human serum butyrylcholinesterase (approximately 90-kDa subunit) is known to exhibit aryl acylamidase and peptidase activity. Limited alpha-chymotrypsin digestion of the purified butyrylcholinesterase gave three major protein fragments of approximately 50 kDa, approximately 21 kDa and approximately 20 kDa. In our earlier studies [Rao and Balasubramanian (1989) Eur. J. Biochem. 179, 639-644] we characterized the approximately 20-kDa fragment and showed that it exhibited both butyrylcholinesterase and aryl acylamidase activities. In the present studies the approximately 50-kDa fragment is characterized. This fragment, after isolation by Sephadex G-75 chromatography from a chymotryptic digest of purified butyrylcholinesterase, exhibited only peptidase activity and was devoid of cholinesterase and aryl acylamidase activities. It could bind to a column of Ricinus communis agglutinin bound to Sepharose, indicating its glycosylated nature and the presence of galactose. The peptidase activity in the approximately 50-kDa fragment could be immuno-precipitated by a polyclonal antibody raised against purified butyrylcholinesterase. SDS-gel electrophoresis of this fragment isolated by R. communis agglutinin-Sepharose and Sephadex G-75 chromatography showed a protein band of approximately 50 kDa by silver staining. Amino-terminal sequence analysis of the approximately 50-kDa fragment gave the sequence of Gly-Pro-Thr-Val-Asp which corresponded to amino acid residues 291-295 in the butyrylcholinesterase sequence [Lockridge et al. (1987) J. Biol. Chem. 262, 549-557]. The combined results suggested that alpha-chymotrypsin digestion of human serum butyrylcholinesterase resulted in the formation of a approximately 20-kDa fragment exhibiting both cholinesterase and aryl acylamidase activities and a approximately 50-kDa fragment exhibiting only peptidase activity.

Characterization of a pseudocholinesterase purified from surgeonfish tissues confirms the atypical nature of this enzyme

The sialated, presumed-globular form of an atypical pseudocholinesterase (pseudo-ChE) previously described from surgeonfish tissues (Leibel: Comparative Biochemistry and Physiology 1988) has been purified to apparent homogeneity using a combination of salt fractionation along with ion-exchange and concanavalin A-Sepharose affinity chromatographic techniques. An overall 1,400-fold purification has been achieved with a 24% final yield of a cholinesterase (ChE) whose final specific activity is 50 mumol/min-mg. The purified enzyme was subjected to detailed biochemical and physical analysis. The purified pseudo-ChE is a sialated, globular, tetrameric enzyme with an apparent sedimentation coefficient of 11.5 S (+/- 0.5 S) and a molecular weight of 250 kilodaltons. The monomers are apparently not secured by disulfide bridges. The enzyme preferentially hydrolyzes acetyl(thio)choline but also hydrolyzes propionyl(thio)choline at reduced but comparable rates along with a wide variety of other noncholine esters. As such, it demonstrates the relative nonspecificity associated with classical pseudo-ChEs. However, the enzyme exhibits limited, but real, substrate inhibition with all choline esters as does true acetylcholinesterase (AChE). The enzyme is insensitive to the AChE inhibitor BW 284C51, sensitive to one (RO2-0683) of two (RO2-1250) pseudo-ChE inhibitors, and particularly sensitive to paraoxon inhibition (10(3)-10(4)-fold more so than AChE). It exhibits the short thermal half-life characteristic of pseudo-ChEs but not the expected ionic activation/inhibition profile. It is clear from this and other studies of atypical extrasynaptic cholinesterase activities occurring in other vertebrates that the orthodox categorization of cholinesterase as either "true" ("specific"; E.C. 3.1.1.7) or "pseudo" ("nonspecific"; E.C. 3.1.1.8) is inadequate to accommodate the increasing instances of ChE activities that exhibit atypical, intermediate properties.

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.

An analysis of esterase activities from surgeonfish tissues yields evidence of an atypical pseudocholinesterase

1. Esterases from tissues of the surgeonfish (Teleostei, Perciformes, Acanthuridae) are characterized electrophoretically and include several carboxylesterases, an acetylesterase, and an atypical pseudocholinesterase (pseudo-ChE). 2. The pseudo-ChE occurs in several isozymic forms including sialated and asialated slightly-anodal forms found principally in liver, and a larger, asialated asymmetric form that barely penetrates the 10% PAGE gel matrix found together with true AChE in epaxial muscle, brain, and eye. 3. Characterization of these three pseudo-ChE activities suggest that they are decidedly atypical in the intermediacy of their substrate and inhibitor specificities relative to classically-defined AChE and pseudo-ChE activities.

Distributions of molecular forms of acetylcholinesterase and butyrylcholinesterase in nervous tissue of the cat

We analyzed the activities of acetylcholinesterase and butyrylcholinesterase, and of the metabolic enzymes enolase and lactate dehydrogenase, in the superior cervical ganglion, ciliary ganglion, dorsal root ganglion, stellate ganglion, and caudate nucleus of the cat; we found that these tissues possess very different levels of enzymic activities. The proportions of the alpha alpha, alpha gamma, and gamma gamma enolase isozymes are also quite variable. We particularly studied the molecular forms of acetylcholinesterase and butyrylcholinesterase, in normal tissues and in preganglionically denervated SCG, in comparison with earlier histochemical findings. The results are consistent with the premise that the G1 (globular monomer) forms of both enzymes are located in the cytoplasm, the G4 (globular tetramer) forms are at the plasma membranes, and the A12 (collagen-tailed, asymmetric dodecamer) form of acetylcholinesterase is at synaptic sites.

Horse serum butyrylcholinesterase kinetics: a molecular mechanism based on inhibition studies with dansylaminoethyltrimethylammonium

The kinetics of the hydrolysis of butyrylthiocholine by horse serum butyrylcholinesterase (acylcholine acylhydrolase; BuChE; EC 3.1.1.8) exhibit an activation phenomenon at high substrate concentrations. At least two mechanistic models can account for the enzyme kinetics: one assumes the binding of an additional substrate molecule on the acyl-enzyme intermediate, and the other hypothesizes the existence of a peripheral regulatory site for the substrate. (1-Dimethylaminonaphthalene-5-sulfonamidoethyl)-trimethylammonium perchlorate, a potent reversible inhibitor, appears to affect BuChE activity by binding to a peripheral site. The inhibition is of the mixed type at low substrate concentrations and of the competitive type at high substrate concentrations. This is consistent with a peripheral site for the binding of the substrate responsible for the activation phenomenon.

Molecular forms of sucrose extractable and particulate acetylcholinesterase in the developing and adult rat brain

The activity of acetylcholinesterase in the rat striatum increased considerably during development, while activities in the cerebellum and midbrain increased only slightly. During maturation the activity of butyrylcholinesterase increased in all the brain regions examined except in cerebellum. The percentage of acetylcholinesterase extractable by isotonic sucrose solution from mature striatum was much smaller than those obtained for other regions of the rat brain. For the developing striatum, the percentage of isotonic sucrose extractable activity was almost three times that for adult striatum. Density gradient centrifugation showed that the membrane-bound particulate fraction of adult rat brain was mostly composed of the 10 S form of acetylcholinesterase with little activity of 4 S form of the enzyme. However, a much higher proportion of the 4S form was found in the isotonic sucrose soluble fraction. In contrast to the particulate fraction from adult brain, that from 6-day old rats contained a much higher proportion of the 4 S form of the enzyme. The sucrose soluble fraction from 6-day old rat brains contained in general much smaller proportion of 4S form as compared to those from adult rat brains.

Amino acid sequence of the active site of human pseudocholinesterase

The usual E1u and atypical E1a human pseudocholinesterases (acylcholine acylhydrolase, EC 3.1.1.8) were purified to homogeneity. The active-site serine residue was conjugated with diisopropyl fluorophosphate and digested with trypsin. The tryptic peptide containing the active site was isolated by gel filtration followed by two-dimensional paper chromatography and electrophoresis. The amino acid sequence of the active site peptide obtained from the usual E1u enzyme was found to be Gly-Glu-Ser-Ala-Gly-Ala-Ser-Ala-Val-Ser-Leu. A remarkable structural homology exists between the human and the horse enzymes in their active sites. From the difference in electrophoretic mobility of the active-site peptides obtained from the usual and atypical enzymes, the probable structure of the atypical human enzyme was deduced as Gly-His-Ser-Ala-Gly-Ala-Ser-Ala-Val-Ser-Leu.

[Multiple molecular forms of human plasma butyrylcholinesterase. II.-Study of the C1, C3 and C4 components by means of affinity electrophoresis (author's transl)]

Affinity electrophoresis has been applied to the analysis of the multiple molecular forms of human plasma cholinesterase allozyme U. A water-soluble p-amino-substituted-phenyltrimethylammonium polyacrylamide was synthetized by copolymerization of an unsaturated derivative of the ligand with acrylamide, and entrapped at various concentrations within the matrix of separating gels. Electrophoresis was carried out in these gels, and the relative mobility of the molecular forms of the enzyme was decreased. From the variation of mobility (Rm) as a function of immobilized ligand concentrations, the apparent dissociation constants of monomer (C1), dimer (C3) and tetramer (C4) of phenotype U were calculated. The decrease in mobility was reversed by addition of non-immobilized competitive ligands (N-methylpyridinium and N-methylacridinium). The appearance of the slopes of Rmi-1 vs. concentration does not give sufficient information for determination of the number of anionic binding sites of C4, but the slight curvature of the plots suggests that bivalent or higher interactions occur when the concentration is sufficiently high. For all three size isomers from a critical ligand concentration, a second zone, named B, appears and intensifies rapidly at the expense of the first zone (A) as the immobilized ligand concentration increases. Among several possible explanations of this phenomenon, it is proposed that the ligand induces a conformational isomerization of the enzymes with a change in affinity (KD,B less than KD,A) and that the interconversion process between the two states B in equilibrium A is slow compared with the ligand-association equilibrium dissociation steps.

Acetylcholinesterase and butyrylcholinesterase measurement in the pre-natal detection of neural tube defects and other fetal malformations

Acetylcholinesterase activity in amniotic fluid was measured at 30 degree C by a reaction rate method employing acetyl-beta-methyl thiocholine as substrate and ethopropazine as a selective inhibitor of butyrylcholinesterase. This assay proved more specific than previously reported methods. Activity was greater in five cases of anencephaly (4.8-9.7 U/l) and nine cases of spinal bifida (5.1-8.6 U/l) than in 50 pregnancies with normal outcome (mean activity 2.0 +/- 0.9 (S.D.) U/l). There was no overlap between results from normal and neural-tube-defect groups, and the results showed no significant correlation with gestational age. Butyrylcholinesterase activity in amniotic fluid was measured using butyrylthiocholine as substrate. In accordance with previous reports, levels were elevated in pregnancies affected by neural tube defects. The ratio butyrylcholinesterase/acetylcholinesterase activity showed similar values for anencephalic, spina bifida and normal pregnancies; however, the two cases of exomphalos investigated could be clearly distinguished from all other groups on this basis.

[Purification of butyrylcholinesterase from human plasma]

Human plasma butyrylcholinesterase (E.C.3.1.1.8) was highly purified by a three-step procedure involving affinity and ion-exchange chromatography techniques. The final product was about 15,000-fold purified with a yield of 12% and a specific activity of 450 U/mg.

Histoenzymological compartmentation of butyryl cholinesterase in the Glossimetra orientalis Mehra 1937

Butyryl cholinesterase activity in Glossimetra orientalis was studied histochemically with Gomori's method using butyrylthiocholine as substrate. Eserine sulphate (10(-5) M) was used as inhibitor for AChE. The study reveals that the enzyme is present mainly in the musculature of the reproductive system, excretory canal, nerve cells and fibers, tegument and subtegumentary cells and suckers. The testes, ovary and parenchyma are completely negative. The functional significance of the enzyme in the various locations have been discussed.

Identification of acylcholine acyl-hydrolase with carboxylic ester-hydrolase in human serum

The relationship between pseudocholine esterase [acylcholine acyl-hydrolase, EC 3.1.1.8] and non-specific esterase [carboxylic ester-hydrolase, EC 3.1.1.1] in human serum was investigated. The purified preparation (purified 500-fold) which had both pseudocholine esterase and non-specific esterase activities, was found to give a single band with faint tailing on polyacrylamide gel electrophoresis. The ratio of the specific activity of pseudocholine esterase to that of non-specific esterase remained essentially the same during the purification procedures. Furthermore, the pseudocholine esterase was demonstrated to be identical with the non-specific esterase by immunochemical studies. All these results suggest that activities of pseudocholine esterase and non-specific esterase in human serum derive from the same enzyme molecule. Observation of Yoshida-cho in Ehime after the application of organophosphorus insecticide supported our results: the activity of pseudocholine esterase was found to be reduced with a concomitant decrease in the activity of non-specific esterase. Based on these results, the physiological significance of the esterase is discussed.