Amphiphilic and hydrophilic forms of acetylcholinesterase from sheep platelets

Acetylcholinesterase from Human Erythrocytes as a Surrogate Biomarker of Lead Induced Neurotoxicity

Lead induced neurotoxicity in the people engaged in different occupations has received wide attention but very little studies have been carried out to monitor occupational neurotoxicity directly due to lead exposure using biochemical methods. In the present paper an endeavour has been made in order to assess the lead mediated neurotoxicity by in vitro assay of the activity of acetylcholinesterase (AChE) from human erythrocytes in presence of different concentrations of lead. The results suggested that the activity of this enzyme was localized in membrane bound fraction and it was found to be highly stable up to 30 days when stored at -20°C in phosphate buffer (50 mM, pH 7.4) containing 0.2% Triton X-100. The erythrocyte's AChE exhibited K m for acetylcholinesterase to be 0.1 mM. Lead caused sharp inhibition of the enzyme and its IC50 value was computed to be 1.34 mM. The inhibition of the enzyme by lead was found to be of uncompetitive type (K i value, 3.6 mM) which negatively influenced both the V max and the enzyme-substrate binding affinity. Taken together, these results indicate that AChE from human erythrocytes could be exploited as a surrogate biomarker of lead induced neurotoxicity particularly in the people occupationally exposed to lead.

PTPN13 regulates cellular signalling and β-catenin function during megakaryocytic differentiation

PTPN13 is a high-molecular weight intracellular phosphatase with several isoforms that exhibits a highly modular structure. Although in recent years different roles have been described for PTPN13, we are still far from understanding its function in cell biology. Here we show that PTPN13 expression is activated during megakaryocytic differentiation at the protein and mRNA level. Our results show that the upregulation of PTPN13 inhibits megakaryocytic differentiation, while PTPN13 silencing triggers differentiation. The ability of PTPN13 to alter megakaryocytic differentiation can be explained by its capacity to regulate ERK and STAT signalling. Interestingly, the silencing of β-catenin produced the same effect as PTPN13 downregulation. We demonstrate that both proteins coimmunoprecipitate and colocalise. Moreover, we provide evidence showing that PTPN13 can regulate β-catenin phosphorylation, stability and transcriptional activity. Therefore, the ability of PTPN13 to control megakaryocytic differentiation must be intimately linked to the regulation of β-catenin function. Moreover, our results show for the first time that PTPN13 is stabilised upon Wnt signalling, which makes PTPN13 an important player in canonical Wnt signalling. Our results show that PTPN13 behaves as an important regulator of megakaryocytic differentiation in cell lines and also in murine haematopoietic progenitors. This importance can be explained by the ability of PTPN13 to regulate cellular signalling, and especially through the regulation of β-catenin stability and function. Our results hold true for different megakaryocytic cell lines and also for haematopoietic progenitors, suggesting that these two proteins may play a relevant role during in vivo megakaryopoiesis.

The use of cholinesterases in ecotoxicology

Cholinesterase (ChE) is one of the most employed biomakers in environmental analysis. Among ChEs, potentially the most significant in environmental terms is acetylcholinesterase (AChE), an enzymatic form that terminates the nerve impulse . Because of its physiological role, Ache has long been considered a highly specific biomarker for organisms exposed to anticholinesterasic agents, primarily agro-chemicals (organophosphate and carbamate pesticides). The effects of these pesticides depends upon their selective inhibition of AChE. Because large amounts of such pesticides are employed, it is plausible that they exert neurotoxic effects on some non-target species. Therefore, AChE is among the most valuable of diagnostic tools that can be used to verify exposure to such chemical agents. It is well known that assays are available for use quantifying AChE in multiple tissues of several test organisms. Enzymes other than AChE (e.g., butyrylcholinesterase and carboxylesterases) have also been used as putative markers for detecting the environmental presence of contaminating compounds. Researchers must use a step-by-step approach to identify the most prominent cholinesterasic form present in a given species, so that this form can be distinguished from others that may interfere with its use. Such fundamental work must be completed prior to using ChEs for any monitoring to assess for anticholinesterasic effects. Despite massive employment in environmental analysis, using ChE inhibition as an endpoint or effect criterion has been unsettled by the discovery the ChEs may interact in the environmental in previously unknown ways. Several chemicals, in addition to anticholinesterasic pesticides, are now known to inhibit ChE activity. Such chemical include detergents, metals, and certain organic compounds such as hydrocarbons. The situation is made worse, because the literature is contradictory as to the ability of such chemicals and elements to interact with ChEs. Some results indicate that ChE inhibition by metals, detergents , and complex mixtures do not or are unlikely to occur. These problems and contradictions are addressed in this review. It is purpose in this review to address the following practical issues related to the ChEs: 1. The situation and organisms in which ChEs have been employed as biomarkers in laboratory trials, and the need to fully characterize these enzymatic forms before they are used for environmental assessment purposes. 2. The ways in which ChEs have been used in field monitoring, and the potential for use of others complimentary markers to diagnose organophosphate exposure, and how drawbacks (such as the absence of reference values) can be overcome. 3. What requirements must be satisfied prior implementing the use of ChEs as biomarkers in species not yet studied. 4. How direct linkages have been established between ChE inhibition and effects from inhibition observed at higher levels of integration (e.g., behavioral changes and population effects, or others indices of ecological relevance). 5. The potential for ChE inhibition to be applied as an effective parameter of toxicity to detect for the environmental presence of compounds other than the organo-phosphate and carbamate pesticides, and the limitations associated therewith.

Existence of two membrane-bound acetylcholinesterases in the honey bee head

Two acetylcholinesterase (EC 3.1.1.7) membrane forms AChE(m1) and AChE(m2), have been characterised in the honey bee head. They can be differentiated by their ionic properties: AChE(m1) is eluted at 220 mM NaCl whereas AChE(m2) is eluted at 350 mM NaCl in anion exchange chromatography. They also present different thermal stabilities. Previous processing such as sedimentation, phase separation, and extraction procedures do not affect the presence of the two forms. Unlike AChE(m1), AChE(m2) presents reversible chromatographic elution properties, with a shift between 350 to 220 mM NaCl, depending on detergent conditions. Purification by affinity chromatography does not abolish the shift of the AChE(m2) elution. The similar chromatographic behaviour of soluble AChE strongly suggests that the occurrence of the two membrane forms is not due to the membrane anchor. The two forms have similar sensitivities to eserine and BW284C51. They exhibit similar electrophoretic mobilities and present molecular masses of 66 kDa in SDS-PAGE and a sensitivity to phosphatidylinositol-specific phospholipase C in non-denaturing conditions, thus revealing the presence of a glycosyl-phosphatidylinositol anchor. We assume that bee AChE occurs in two distinct conformational states whose AChE(m2) apparent state is reversibly modulated by the Triton X-100 detergent into AChE(m1).

Muscular dystrophy alters the processing of light acetylcholinesterase but not butyrylcholinesterase forms in liver of Lama2(dy) mice

In order to know whether the histopathological changes of liver, which accompany muscular dystrophy, affect the synthesis of cholinesterases, the distribution and glycosylation of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) forms in normal (NL) and dystrophic Lama2(dy) mouse liver (DL) were investigated. About half of liver AChE, and 25% of BuChE were released with a saline buffer (fraction S(1)), and the rest with a saline-Brij 96 buffer (S(2)). Abundant light (G(2)(A) and G(1)(A)) AChE (87%) and BuChE (93%) forms, and a few G(4)(H) and G(4)(A) ChE species were identified in liver. The dystrophic syndrome had no effect on solubilization or composition of ChE forms. Most of the light AChE and BuChE species (>95%) were bound by octyl-Sepharose, while most light AChE forms (80%), but not BuChE isoforms (15%), were retained in phenyl-agarose. About half of the AChE dimers lost their amphiphilic anchor with phosphatidylinositol-specific phospholipase C (PIPLC), and the fraction of PIPLC-resistant species increased in DL. AChE T and R transcripts were detected by reverse transcriptase-polymerase chain reaction (RT-PCR) of liver RNA. ChE components of liver, erythrocyte, and plasma were distinguished by their amphiphilic properties and interaction with lectins. The dystrophic syndrome increased the liver content of the light AChE forms with Lens culinaris agglutinin (LCA) reactivity. The abundance of ChE tetramers in plasma and their small amount in liver suggest that after their assembly in liver they are rapidly secreted, while the light species remain associated to hepatic membranes.