Development of potent reversible selective inhibitors of butyrylcholinesterase as fluorescent probes

Brain butyrylcholinesterase (BChE) is an attractive target for drugs designed for the treatment of Alzheimer's disease (AD) in its advanced stages. It also potentially represents a biomarker for progression of this disease. Based on the crystal structure of previously described highly potent, reversible, and selective BChE inhibitors, we have developed the fluorescent probes that are selective towards human BChE. The most promising probes also maintain their inhibition of BChE in the low nanomolar range with high selectivity over acetylcholinesterase. Kinetic studies of probes reveal a reversible mixed inhibition mechanism, with binding of these fluorescent probes to both the free and acylated enzyme. Probes show environment-sensitive emission, and additionally, one of them also shows significant enhancement of fluorescence intensity upon binding to the active site of BChE. Finally, the crystal structures of probes in complex with human BChE are reported, which offer an excellent base for further development of this library of compounds.

Oligomerization status influences subcellular deposition and glycosylation of recombinant butyrylcholinesterase in Nicotiana benthamiana

Plants have a proven track record for the expression of biopharmaceutically interesting proteins. Importantly, plants and mammals share a highly conserved secretory pathway that allows similar folding, assembly and posttranslational modifications of proteins. Human butyrylcholinesterase (BChE) is a highly sialylated, tetrameric serum protein, investigated as a bioscavenger for organophosphorous nerve agents. Expression of recombinant BChE (rBChE) in Nicotiana benthamiana results in accumulation of both monomers as well as assembled oligomers. In particular, we show here that co-expression of BChE with a novel gene-stacking vector, carrying six mammalian genes necessary for in planta protein sialylation, resulted in the generation of rBChE decorated with sialylated N-glycans. The N-glycosylation profile of monomeric rBChE secreted to the apoplast largely resembles the plasma-derived orthologue. In contrast, rBChE purified from total soluble protein extracts was decorated with a significant portion of ER-typical oligomannosidic structures. Biochemical analyses and live-cell imaging experiments indicated that impaired N-glycan processing is due to aberrant deposition of rBChE oligomers in the endoplasmic reticulum or endoplasmic-reticulum-derived compartments. In summary, we show the assembly of rBChE multimers, however, also points to the need for in-depth studies to explain the unexpected subcellular targeting of oligomeric BChE in plants.

Crystallization and X-ray structure of full-length recombinant human butyrylcholinesterase

Human butyrylcholinesterase (BChE) has been shown to function as an endogenous scavenger of diverse poisons. BChE is a 340 kDa tetrameric glycoprotein that is present in human serum at a concentration of 5 mg l(-1). The well documented therapeutic effects of BChE on cocaine toxicity and organophosphorus agent poisoning has increased the need for effective methods of producing recombinant therapeutic BChE. In order to be therapeutically useful, BChE must have a long circulatory residence time or associate as tetramers. Full-length recombinant BChE produced in Chinese hamster ovary (CHO) cells or human embryonic kidney cells has been shown to associate as monomers, with a shorter circulatory residence time than the naturally occurring tetrameric serum protein. Based on the preceding observation as well as the need to develop novel methodologies to facilitate the mass production of therapeutic recombinant BChE, studies have been initiated to determine the structural basis of tetramer formation. Towards these ends, full-length monomeric recombinant BChE has been crystallized for the first time. A 2.8 A X-ray structure was solved in space group P42(1)2, with unit-cell parameters a = b = 156, c = 146 A.

Recombinant human butyrylcholinesterase from milk of transgenic animals to protect against organophosphate poisoning

Dangerous organophosphorus (OP) compounds have been used as insecticides in agriculture and in chemical warfare. Because exposure to OP could create a danger for humans in the future, butyrylcholinesterase (BChE) has been developed for prophylaxis to these chemicals. Because it is impractical to obtain sufficient quantities of plasma BChE to treat humans exposed to OP agents, the production of recombinant BChE (rBChE) in milk of transgenic animals was investigated. Transgenic mice and goats were generated with human BChE cDNA under control of the goat beta-casein promoter. Milk from transgenic animals contained 0.1-5 g/liter of active rBChE. The plasma half-life of PEGylated, goat-derived, purified rBChE in guinea pigs was 7-fold longer than non-PEGylated dimers. The rBChE from transgenic mice was inhibited by nerve agents at a 1:1 molar ratio. Transgenic goats produced active rBChE in milk sufficient for prophylaxis of humans at risk for exposure to OP agents.

Human serum cholinesterase from liver pathological samples exhibit highly elevated aryl acylamidase activity

BACKGROUND

Although aspartate aminotransferase (AST) and gamma-glutamyltransferase (gamma GT) enzymes are widely used as markers for liver disorders, the ubiquitous enzyme butyrylcholinesterase (BChE), synthesized in liver is also used as marker in the assessment of liver pathophysiology. This BChE enzyme in addition to its esterase activity has yet another enzymatic function designated as aryl acylamidase (AAA) activity. It is determined in in vitro based on the hydrolysis of the synthetic substrate o-nitroacetanilide. In the present study, human serum cholinesterase (BChE) activity was studied with respect to its AAA activity on the BChE protein (AAA(BChE)) in patients with liver disorders. AST and gamma GT values were taken into account in this study as known markers for liver disorders.

METHODS

Blood samples were grouped into 3 based on esterase activity associated with BChE protein. They are normal, low, and very low BChE activity but with markedly increased AST and gamma GT levels. These samples were tested for their respective AAA function. Association of AAA with BChE from samples was proved using BChE monoclonal antibody precipitation experiment.

RESULTS

The absolute levels of AAA were increased as BChE activity decreased while deviating from normal samples and such deviation was directly proportional to the severity of the liver disorder. Differences between these groups became prominent after determining the ratios of AAA(BChE) to BChE activities. Samples showing very high AAA(BChE) to BChE ratio were also showing high to very high gamma GT values.

CONCLUSIONS

These findings establish AAA(BChE) as an independently regulated enzymatic activity on BChE especially in liver disorders. Moreover, since neither the low esterase activity of BChE by itself nor increased levels of AST/gamma GT are sufficient pathological indicators, this pilot study merits replication with large sample numbers.

Butyrylcholinesterase activity and molecular components in thymus of healthy and merosin-deficient Lama2dy mice

The laminin-alpha2 chain, referred to as merosin, forms part of the laminin-2 heterotrimer (alpha2beta1gamma1), which is principally expressed in the basement membrane of muscle. Nearly half of patients suffering from congenital muscular dystrophy (CMD) have abnormalities in the laminin-alpha2 chain (LAMA2) gene, and the merosin-deficient Lama2dy mouse shows CMD. The expression of merosin in thymus, the abnormalities in the gland of Lama2dy mice, and the presence of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in thymus prompted us to study the possible effects of the deficiency of merosin on thymus BuChE. We found that, while AChE activity decreased by approximately 50% in merosin-deficient thymus, the deficiency had little effect on BuChE activity. About 65% of thymus BuChE activity was extracted with a saline buffer and 30% with 1% Triton X-100. Sedimentation analyses and phenyl-agarose chromatography showed that thymus contained amphiphilic BuChE monomers (G(1)(A),44%) and dimers (G(2)(A),33%), and hydrophilic tetramers (G(4)(H),23%). Binding assays with various plant lectins revealed differences between the oligoglycans linked to BuChE tetramers and lighter components. The deficiency of merosin had no effect on the biosynthesis of thymus BuChE as judged by the lack of major changes between control and Lama2dy mice thymuses in the distribution of BuChE molecules and the level of lectin binding. The detoxifying action of BuChE, its role as a backup to AChE, and the relevance of the cholinergic dialogue between T cells and stromal cells for T lymphocyte proliferation, maturation and survival support a physiological function for BuChE in thymus.

A novel butyrylcholinesterase from serum of Leporinus macrocephalus, a Neotropical fish

We show here that serum of piaussu, a Neotropical characin fish, has the highest butyrylcholinesterase activity so far described for humans and fish. To clarify whether this cholinesterase could protect piaussu against anticholinesterase pesticides by scavenging organophosphates, we purified it 1700-fold, with a yield of 80%. Augmenting concentrations (from 0.01 to 20 mM) of butyrylthiocholine activated it. The pure enzyme was highly inhibited by chlorpyriphos-oxon (ki=10,434x10(6) M-1 min-1) and by the specific butyrylcholinesterase inhibitor, isoOMPA (ki=45.7x10(6) M-1 min-1). Electrophoresis of total serum and 2-D electrophoresis of the purified cholinesterase showed that some enzyme molecules could circulate in piaussu serum as heterogeneously glycosylated dimers. The enzyme's N-terminal sequence was similar to sequences found for butyrylcholinesterase from sera of other vertebrates. Altogether, our data present a novel butyrylcholinesterase with the potential of protecting a fish from poisoning by organophosphates.

Polyethylene glycosylation prolongs the circulatory stability of recombinant human butyrylcholinesterase

Previous studies in rodents and non-human primates have demonstrated that pretreatment of animals with cholinesterases could provide significant protection against organophosphate (OP) nerve agent toxicity. Gene delivery/therapy is emerging as an approach to achieve high-level expression of proteins in vivo that are very similar to their native counterparts. Recently, adenoviral (Ad) vectors have proven to be excellent vehicles for delivering genes to cells in vitro and in vivo. In this study, we explored the use of the newly designed AdenoVATOR system for the expression of recombinant human butyrylcholinesterase (rHu BChE) in human embryonic kidney 293A (HEK-293A) cells. In these cells, rHu BChE was expressed as mostly tetrameric form by the simultaneous expression of proline-rich attachment domain. By optimizing the culture conditions, 1.5-2.0 U/ml of rHu BChE could be expressed in HEK-293A cells. Recombinant Hu BChE was purified to homogeneity by ammonium sulfate fractionation followed by affinity column chromatography using procainamide Sepharose and cobalt Sepharose gels. The enzymatic and physico-chemical properties of purified rHu BChE were similar to those of native serum-derived Hu BChE. To determine the suitability of this preparation for use as an antidote against highly toxic nerve agents, its pharmacokinetics were evaluated in mice. Recombinant Hu BChE exhibited a mean residence time of 18.3 h which was 2.5-fold shorter than that observed for native Hu BChE in mice. However, rHu BChE chemically modified with polyethyleneglycol (PEG) displayed a mean residence time of 36.2 h suggesting that PEG-modification can prolong the circulatory stability of rHu BChE. The efficacy of Ad-Hu BChE to induce the production of therapeutic levels of bioscavenger in vivo is under evaluation.

Partial Purification and Characterization of Soluble Isoform of Butyrylcholinesterase from Rat Intestine

Butyrylcholinesterase (BChE; E.C. 3.1.1.8.) was 260-fold purified from soluble fraction of rat intestine. The enzyme was composed of tetrameric globular form by nonreducing electrophoresis. Optimum pH value was determined as 7.2 after zero buffer extrapolation. Optimum temperature was examined as 37 degrees C after zero time extrapolation. The enzyme showed marked substrate activation with positively charged, acyl-choline substrates. As a measure of catalytic efficiency, kcat/Km values were determined as 16,210, 25,650, and 46,150 for acetylthiocholine (ATCh), propionylthiocholine (PTCh), and butyrylthiocholine (BTCh), respectively. When the catalytic efficiencies are compared, soluble isoform of rat intestinal BChE became increasingly efficient as the size of the acyl portion of the substrate increases; BTCh > PTCh > ATCh. Differently, the enzyme showed substrate inhibition with benzoylcholine (BzCh) and a kcat/Km value of 21,190 was found. Triton X-100 inhibited more efficiently the rat intestinal BChE soluble isoform than it did the human serum BChE.

Automated measurement of acetylcholinesterase activity in rat peripheral tissues

The accepted mechanism of toxicity of many organophosphorous and carbamate insecticides is inhibition of acetylcholinesterase activity. In mammals, part of the toxicity assessment usually includes monitoring blood and/or brain acetylcholinesterase inhibition. Other tissues, however, contain cholinesterase activity (i.e. acetyl- and butyryl-cholinesterase), and the inhibition of that activity may be informative for a full appraisal of the toxicity profile. The present group of studies first optimized the variables for extraction and solubilization of cholinesterase activity from various rat tissues and then refined an existing automated method, in order to differentially assess acetyl and butyrylcholinesterase activity in those tissues. All these studies were conducted using tissues from untreated, Long-Evans, adult rats. The first studies determined the effect of Triton X-100 or salt (NaCl) on the extraction and solubilization of cholinesterase activity from retina, brain, striated muscle, diaphragm, and heart: phosphate buffer plus detergent (1% Triton X-100) yielded the highest activity for most tissues. For striated muscle, however, slightly more activity was extracted if the phosphate buffer contained both 1% Triton X-100 and 0.5 M NaCl. It was also noted that the degree of homogenization of some tissues (e.g. striated muscle) must be increased for maximal solubilization of all cholinesterase activity. Subsequent studies developed a method for assessing the level of acetylcholinesterase, butyrylcholinesterase and total cholinesterase activity in these tissues using an automated analyzer. In conclusion, automated assay of acetylcholinesterase activity in cholinergically innervated tissues in the rat (other than brain) is achievable and relatively convenient.

Identification of hybrid cholinesterase forms consisting of acetyl- and butyrylcholinesterase subunits in human glioma

Brain and non-brain tumors contain acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) transcripts and enzyme activity. AChE and BuChE occur in tissues as a set of molecular components, whose distribution in a cyst fluid from a human astrocytoma we investigated. The fluid displayed high BuChE and low AChE activities. Three types of cholinesterase (ChE) tetramers were identified in the fluid by means of sedimentation analyses and assays with specific inhibitors, and their sedimentation coefficients were 11.7S (ChE-I), 11.1S (ChE-II), and 10.5S (ChE-III). ChE-I was unretained, ChE-II was weakly retained and ChE-III was adsorbed to edrophonium-agarose, confirming the AChE nature of the latter. ChE-I and ChE-II tetramers contained BuChE subunits as shown by their binding with an antiserum against BuChE. The ChE activity of the immunocomplexes made with ChE-II and anti-BuChE antibodies decreased with the AChE inhibitor BW284c51, revealing that ChE-II was made of AChE and BuChE subunits, in contrast to ChE-I, which only contained BuChE subunits. The binding of an anti-AChE antibody (AE1) to ChE-II and ChE-III, but not to ChE-I, demonstrated the hybrid composition of ChE-II. A substantial fraction of the AChE tetramers and dimers of astrocytomas and oligodendrogliomas bound both to anti-AChE and anti-BuChE antibodies, which revealed a mixed composition of AChE and BuChE subunits in them. The AChE components of brain, meningiomas and neurinomas were only recognized by AE1. In conclusion, our results demonstrate that aberrant ChE oligomers consisting of AChE and BuChE subunits are generated in astrocytomatous cyst and gliomas but not in brain, meningiomas or neurinomas.

Engineering of a monomeric and low-glycosylated form of human butyrylcholinesterase: expression, purification, characterization and crystallization

Human butyrylcholinesterase (BChE; EC 3.1.1.8) is of particular interest because it hydrolyzes or scavenges a wide range of toxic compounds including cocaine, organophosphorus pesticides and nerve agents. The relative contribution of each N-linked glycan for the solubility, the stability and the secretion of the enzyme was investigated. A recombinant monomeric BChE lacking four out of nine N-glycosylation sites and the C-terminal oligomerization domain was stably expressed as a monomer in CHO cells. The purified recombinant BChE showed catalytic properties similar to those of the native enzyme. Tetragonal crystals suitable for X-ray crystallography studies were obtained; they were improved by recrystallization and found to diffract to 2.0 A resolution using synchrotron radiation. The crystals belong to the tetragonal space group I422 with unit cell dimensions a = b = 154.7 A, c = 124.9 A, giving a Vm of 2.73 A3 per Da (estimated 60% solvent) for a single molecule of recombinant BChE in the asymmetric unit. The crystal structure of butyrylcholinesterase will help elucidate unsolved issues concerning cholinesterase mechanisms in general.

Increased butyrylcholinesterase levels in microsomal membranes of dystrophic Lama2dy mouse muscle

The proportions and the glycosylation of butyrylcholinesterase (BuChE) forms in vesicles rich in sarcoplasmic reticulum from normal (NMV) and dystrophic (DMV) muscle were analyzed, using merosin-deficient dystrophic mice. BuChE activity in DMV was two- to threefold that in NMV. Globular amphiphilic G1A, G2A, and G4A and hydrophilic G4H BuChE forms were identified in NMV and DMV. The amount of G2A forms increased sevenfold in DMV, and the other forms increased about twofold. The higher BuChE level in DMV might reflect a maturational defect, with dystrophy preventing the down-regulation of BuChE with muscle development. About half of G1A, G2A, and G4H BuChE forms in NMV or DMV bound to Lens culinaris agglutinin (LCA), a higher fraction to wheat germ agglutinin (WGA), and little to Ricinus communis agglutinin (RCA). Most of the G4A forms in NMV or DMV bound to LCA or WGA; those from NMV failed to bind to RCA, whereas most of the variants in DMV bound to it, suggesting that the excess of tetramers in DMV is mainly RCA-reactive. The differential interaction of lectins with BuChE components from muscle microsomes, serum, and nerves confirmed that the microsomal BuChE was muscle-intrinsic. The results provide clues regarding the alterations that dystrophy produces in the biosynthesis of BuChE forms in muscle.

Characterization of acetylcholinesterase and butyrylcholinesterase forms in normal and dystrophic Lama2dy mouse heart

In searching for possible differences in acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) forms of dystrophic heart, the properties of ChE species in normal (NH) and dystrophic Lama2dy mouse heart (DH) were investigated. BuChE predominated over AChE. Loosely- and tightly-bound ChEs were released with saline (extract S1) and saline-Triton X-100 buffers (S2). About 50% of AChE, and 25% of BuChE, in NH or DH was measured in S1, and the rest in S2. Asymmetric AChE forms A12 (15%) and A8 (11%), globular hydrophilic G(H)4 (8%), amphiphilic G(A)4 (15%), and G(A)2+G(A)1 (51%) AChE species, and BuChE forms G(H)4 (13%), G(A)4 (3%), and G(A)2+G(A)1 (84%) were identified in NH and DH. Most of the asymmetric and G(A)4 AChE species were bound to Triticum vulgaris (WGA) or Ricinus communis (RCA) agglutinins. About half of G(H)4 and G(A)2+G(A)1 AChE were bound to WGA, and less (10%) to RCA. Variable amounts of G(H)4+G(A)4 (60%), and G(A)2+G(A)1 (75%) BuChE bound to WGA, and 50 and 10% to RCA. The lack of structural differences between ChE species in NH and DH indicates that, in contrast to the ChE forms in mouse skeletal muscle, the biosynthesis of ChE components in heart is not disturbed by dystrophy.

Butyrylcholinesterase is complexed with transferrin in chicken serum

The function of the enzyme butyrylcholinesterase (BChE) both in serum and in brain is unclear. In serum, BChE has been found complexed with several biomedically relevant proteins, with which it could function in concert. Here, the existence of a similar complex formed between BChE and sero-transferrin from adult chicken serum was elucidated. In order to identify both proteins unequivocally, we improved methods to highly purify the 81-kDa BChE and the coisolated 75-kDa transferrin, which then allowed us to tryptically digest and sequence the resulting peptides. The sequences as revealed for BChE peptides were highly identical to mammalian BChEs. A tight complex formation between the two proteins could be established (a) since transferrin is coisolated along with BChE over three steps including procainamide affinity chromatography, while transferrin alone is not bound to this affinity column, and (b) since imunoprecipitation experiments of whole serum with a transferrin-specific antiserum allows us to detect BChE in the precipitate with the BChE-specific monoclonal antibody 7D11. The possible biomedical implications of a complex between transferrin and BChE which here has been shown to exist in chicken serum are briefly discussed.

Evidence for the presence of a mammalian-like cholinesterase in Paramecium primaurelia (Protista, Ciliophora) developmental cycle

By histochemical and immunohistochemical methods, the presence of cholinergic-like molecules has previously been demonstrated in Paramecium primaurelia, and their functional role in mating-cell pairing was suggested. In this work, both true acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities were electrophoretically investigated, and the presence of molecules immunologically related to BuChE was checked by immunoblotting. The AChE activity, shown in the membrane protein fraction of mating-competent cells and in the cytoplasmic fraction of immature cells, is due to a 260-kDa molecular form, similar to the membrane-bound tetrameric form present in human erythrocytes. This AChE activity does not appear in either the cytoplasmic fraction of mating-competent cells or in the membrane protein fraction of immature cells. No evidence was found for the presence or the activity of BuChE-like molecules. The role of AChE in P. primaurelia developmental cycle is discussed.

Aryl acylamidase activity exhibited by butyrylcholinesterase is higher in chick than in horse, but much lower than in fetal calf serum

Several side activities have been attributed to butyrylcholinesterase (BChE), including aryl acylamidase (AAA) activity, which is an amidase-like activity with unknown physiological function splitting the artificial substrate o-nitroacetanilide. For avians, extensive developmental data have pointed to neurogenetic functions of BChE, however, a possible AAA activity of BChE has not been studied. In this study, we first compare the relative levels of AAA exhibited by BChE in whole sera from chick, fetal calves (FCS) and horse. Remarkably, FCS exhibits a 400-fold higher ratio of AAA/BChE than horse and 80-fold higher than chick serum. We then show that an immunoisolated preparation of BChE from chicken serum presents significant activity for AAA. Both in sera and with the purified enzyme, the AAA activity is fully inhibited by anticholinesterase drugs, showing that AAA activity is exclusively conveyed by the BChE molecule. Noticeably, AAA inhibition even occurs at lower drug concentrations than that of BChE activity itself. Moreover, AAA is sensitive to serotonin. These data indicate that (1) AAA is a general feature of serum BChE of vertebrates including avians, (2) AAA is effectively inhibited by cholinergic and serotonergic agents, and (3) AAA may have a developmental role, since it is much pronounced in a serum from fetal animals. Functionally, deamination of neuropeptides, a link between cholinergic and serotonergic neurotransmitter systems, and roles in lipoprotein metabolism could be relevant.

Total syntheses and anticholinesterase activities of (3aS)-N(8)-norphysostigmine, (3aS)-N(8)-norphenserine, their antipodal isomers, and other N(8)-substituted analogues

N(8)-Benzylesermethole (6) was prepared from 5-methoxytryptamine (1) in five steps. Resolution of compound 6 by dibenzoyl- and ditoluyltartaric acid provided enantiomers (-)- and (+)-7. After demethylation, reaction with isocyanates and catalytic debenzylation over hydrogen, the total syntheses of (-)- and (+)-N(8)-norphysostigmine [(-)- and (+)-11] and (-)- and (+)-N(8)-norphenserine [(-)- and (+)-12] were accomplished, (-)-N(8)-Norphysostigmine [(-)-11] and (-)-N(8)-norphenserine [(-)-12] were also obtained by transformations of natural physostigmine [(-)-13] and phenserine [(-)-14] prepared from (-)-13. The absolute configurations and optical purity of compounds (-)-11, (-)-12, (+)-11, and (+)-12 were confirmed by a comparison of their optical rotations with those of the compounds synthesized from physostigmine [(-)-13]. The anticholinesterase activities of N(8)-nor- and N(8)-substituted analogues, (-)- and (+)-9, -10, -11, -12, 15, and 16, were compared with those of physostigmine [(-)- and (+)-13] and phenserine [(-)- and (+)-14] and are reported.

Histidine modification of human serum butyrylcholinesterase

The effects of histidine-modifying reagents on human serum butyrylcholinesterase (BChE) were investigated. The commercially available enzyme was further purified by chromatography on a Sepharose CI-6B column prior to use. In the modification studies, we found that the histidine-specific reagents tosylphenylalanine chloromethyl ketone (TPCK) and tosyllysine chloromethyl ketone (TLCE) did not modify the enzyme; however, they inhibited the enzyme reversibly. The kinetic parameters of enzyme inhibition calculated were alpha = 10.8, beta = 0.26, and Ki = 0.016 mM for TPCK. TLCK inhibition gave similar kinetic behavior, with alpha = 41.6, beta = 0.065, and Ki = 0.039 mM. Tosyllysine, an analog of TLCK, did not inhibit the enzyme. Removal of TPCK and TLCK by dialysis resulted in significant reactivation of the enzyme. From kinetic studies, it was found that the inhibitions were hyperbolic mixed-type inhibitions. We concluded that the reagents competed with substrate for hydrophobic binding sites and inhibited the enzyme reversibly. On the other hand, in the modification studies with diethyl pyrocarbonate (DPC), it was observed that inactivation of the enzyme was irreversible and time-dependent. In the protection studies, the activity of the enzyme was partially protected from inactivation by DPC even at a 50 mM concentration of butyrylthiocholine. The results indicate that DPC modifies some essential histidine side chains in BChE, including the functional histidyl residue found at the active site.

Large-scale purification and long-term stability of human butyrylcholinesterase: a potential bioscavenger drug

Butyrylcholinesterase from human plasma (HuBChE) is a potential drug candidate for detoxification of certain harmful chemicals that contain carboxylic or phosphoric acid ester bonds. Large quantities of purified HuBChE, displaying a high stability upon long-term storage, are required for the evaluation of its therapeutic capacity and its pharmaceutical properties. Several modifications of a previously reported procedure enabled us to purify the enzyme > 15,000-fold from pools of up to 100 1 of human plasma. The three-step procedure is based on precipitation of plasma proteins by ammonium sulfate (step I) and batch adsorption of HuBChE on procainamide-Sepharose 4B gel (step II). Ammonium sulfate was also employed in the third stage to fractionate the final product from procainamide-containing HuBChE solution. The overall yield (63%) of electrophoretically pure enzyme was significantly higher than that previously reported (34%) for the purification of HuBChE from 12.5 1 of plasma or from 5 kg of Cohn fraction IV-4. Purified HuBChE was stored at 5 degrees C in 10 mM phosphate buffer (pH 7.4) containing 1 mM EDTA and 0.02% NaN3. The specific activity, protein migration on gel electrophoresis, thermostability at 54 degrees C and the mean residence time in the circulation of mice remained essentially constant for at least 46 months. The modifications introduced can provide large quantities of purified enzyme that maintains its activity and bioavailability properties for several years.

Evidence for a Zn(2+)-binding site in human serum butyrylcholinesterase

Purified human serum butyrylcholinesterase after treatment with either of the metal chelators EDTA or NaCN was able to bind to a Zn(2+)-chelate-Sepharose affinity column and was eluted from the column by EDTA or imidazole. Prior EDTA treatment of the enzyme was essential for binding to this affinity column. The enzyme could be labelled with (65)Zn(2+) after EDTA treatment of the enzyme. Diethylpyrocarbonate modification of histidine residues in the EDTA-treated enzyme resulted in the abolition of both binding to the Zn(2+)-chelate-Sepharose column and labelling by (65)Zn(2+). Stoicheiometry of (65)Zn(2+) binding indicated approximately 0.85 mol of Zn(2+)/mol of subunit of the EDTA-treated enzyme. EDTA or NaCN treatment resulted in the loss of thermal stability of the enzyme at 37 degrees C which could not be reversed by Zn(2+). Whereas the cholinesterase activity of butyrlcholinesterase was not affected by EDTA, there was significant loss of its carboxypeptidase activity in the presence of EDTA, and the loss could be reversed by added ZnCl2. These results suggest the presence of a Zn(2+)-binding site on human serum butyrylcholinesterase and the involvement of histidine residues in the metal binding. The presence in human serum butyrylcholinesterase of a sequence HXXE...H found in many known Zn(2+)-containing enzymes supports these findings.

Cocaine and butyrylcholinesterase (BChE): determination of enzymatic parameters

In humans, the plasma enzyme, butyrylcholinesterase (E.C. 3.1.1.8), metabolizes cocaine to the water-soluble, pharmacologically inactive compounds, ecgonine methylester and benzoic acid. Homogeneous enzyme was purified from human plasma and used to determine the enzyme kinetic parameters of Km and Vmax with cocaine as the substrate. The KM (11.9 microM) indicates that cocaine is tightly bound to the four active sites of the native tetramer. The Vmax (1.17 microM/min) is 50-fold greater than cocaine catalytic antibodies. Administration of purified human butyrylcholinesterase to a cocaine-intoxicated patient would be expected to shift the metabolism to the inactive metabolites and reduce the toxicity.

Molecular forms of acetyl- and butyrylcholinesterase in normal and dystrophic mouse brain

In searching for possible differences in the composition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) forms in dystrophic brain, the distribution of various enzyme molecules in normal (NB) and dystrophic (DB) 129B6F1/J mouse brain has been investigated. The tissue was sequentially extracted with saline (S1) and with saline-Triton X-100 buffers (S2) to release soluble and membrane-bound cholinesterases. About 15% of the AChE and 35% of the BuChE activities in NB were recovered in S1, and the rest in S2. G4, G2, and G1 AChE and BuChE forms were identified in the soluble fractions obtained from NB and DB. The shift in sedimentation values of the separated AChE and BuChE species in sucrose gradients made with and without detergents revealed the occurrence of hydrophilic (H) and amphiphilic (A) variants of cholinesterases in the extracts. The amphiphilic properties of the several AChE and BuChE molecules were analyzed by Triton X-114 phase-partitioning and by phenyl-agarose chromatography. A12 (1%), G4A (72%), G4H (8%), and G2A + G1A (19%) AChE molecules, and G4A (34%), G4H (19%), and G2A + G1A (47%) BuChE forms, were identified in NB. The G4A AChE and BuChE isoforms differed in their interaction with Triton X-114 and with a hydrophobic matrix. Neither the extent of cholinesterase solubilization, nor the distribution of individual enzyme forms, was significantly altered in DB. The lack of specific differences in the distribution of AChE and BuChE forms between NB and DB suggests that the biosynthetic pathway leading to the various enzyme forms is altered in muscle but not in dystrophic mouse brain.

Acetylcholinesterase and butyrylcholinesterase expression in adult rabbit tissues and during development

A large cDNA fragment covering the complete sequence of the mature catalytic subunit of rabbit acetylcholinesterase (AChE) has been cloned and sequenced. This sequence was compared to that of rabbit butyrylcholinesterase [BChE; Jbilo, O. & Chatonnet, A. (1990) Nucleic Acids Res. 18, 3990]. Amino acid sequences of AChE and BChE have 51% identity. They both possessed a choline-binding site W84, a catalytic triad S200-H440-E327 and six cysteine residues (positions 67-94, 254-265, 402-521) in conserved sequence positions to those that form three intrachain disulfide bonds in all cholinesterases (by convention, numbering of amino acids is that used for Torpedo AChE). Rabbit AChE had a larger number of aromatic residues lining the active-site gorge than rabbit BChE (14 compared to 8, respectively) and a smaller number of potential N-glycosylation sites (3 compared to 8, respectively). Both catalytic subunits have a hydrophilic C-terminus (catalytic subunits of type T). Expression of acetylcholinesterase and butyrylcholinesterase genes (ACHE and BCHE) was studied in rabbit tissues and during development by a correlation of Northern-blot analysis and enzymic activities. This correlation was rendered difficult by the presence of an eserine-resistant esterase active on butyrylthiocholine in serum, liver and lung. When the contribution of this carboxylesterase was taken into account, brain was found as the richest source of BChE followed by lung and heart. Rabbit liver had a very low content of BChE that correlated with the low BChE activity in plasma. During development, BCHE transcripts were detected as early as day 10 post coitum, whereas ACHE transcripts appeared only on day 12.

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.