Behavior Of Acetylcholinesterase Research Articles

Performance Evaluation of Monolith Based Immobilized Acetylcholinesterase Flow-Through Reactor for Copper(II) Determination with Spectrophotometric Detection

A monolith based immobilized acetylcholinesterase (AChE) flow-through reactor has been developed for the determination of copper(II) using flow injection spectrophotometric system. The bioreactor was prepared inside a microcapillary column byin situpolymerization of butyl methacrylate, ethylene dimethacrylate, and 2,2-dimethoxy-1,2-diphynyletane-1-one in the presence of 1-decanol, followed by vinyl azlactone functionalization and AChE immobilization. The behavior of AChE before and after being immobilized on the monolith was evaluated by kinetic parameters from Lineweaver and Burk equation. The detection was based on measuring inhibition effect on the enzymatic activity of AChE by copper(II) using Ellman’s reaction with spectrophotometric detection at 410 nm. The linear range of the calibration graph was obtained over the range of 0.02–3.00 mg L−1. The detection limit, defined as 10% inhibition (I10), was found to be 0.04 mg L−1. The repeatability was 3.35 % (n=5) for 1.00 mg L−1of copper(II). The proposed method was applied to the determination of copper(II) in natural water samples with sampling rate of 4 h−1.

Bifurcation Analysis of a Coupled Acetylcholinesterase/Choline Acetyltransferase Enzymes Neurocycle

A diffusion-reaction, two-compartment model was used to explore the bifurcation and chaotic behavior of acetylcholinesterase (AChE) and cholineacetyltransferase (ChAT) coupled enzymes system. The effects of hydrogen ion feed concentrations, choline (Ch) and acetylcholine (ACh) feed concentrations, as bifurcation parameters on the system performance are studied. It is found that hydrogen ions play an important role in creating potential differences through the plasma membranes. Detailed bifurcation analysis over a wide range of parameters is carried out in order to uncover some of the qualitative changes of the system such as hysteresis, multiplicity, Hopf bifurcation, boundary crises bifurcation, periodic transient, and other complex dynamics. Some of the obtained results relate to the phenomena occurring in the physiological experiments like periodic stimulation of neural cells and irregular functioning of acetylcholine receptors. The model depends on real kinetics expressions and parameters obtained from the literature, so the results can be used to direct more systematic research on cholinergic disorder.

Changes of acetylcholinesterase activity in brain areas and liver of sucrose- and ethanol-fed rats.

The effects of chronic ethanol or sucrose administration to rats on acetylcholinesterase from brain and liver were investigated. Membrane-bound and soluble acetylcholinesterase activities were determined in fractions prepared by centrifugation. The thermal stability and the effects of temperature and different types of alcohols on acetylcholinesterase activity were also studied. Membrane-bound acetylcholinesterase activity increased (p < 0.01) in the liver after chronic ethanol administration, whereas no differences among groups in the encephalic areas, except in the brain stem soluble form, were found. Membrane-bound acetylcholinesterase from the ethanol- and sucrose-treated groups was more stable at the different temperatures assayed between 10 and 50 degrees C than that corresponding to the control group. Non-linear Arrhenius plots were obtained with preparations of membrane-bound acetylcholinesterase from rat liver, with discontinuities at 30 degrees C (control or sucrose groups) or 34-35 degrees C (alcohol group). Assays made with membrane-bound or soluble enzyme from brain showed linear Arrhenius plots in all groups studied. The inhibitory effects of increasing concentrations of ethanol, n-propanol and n-butanol on acetylcholinesterase preparations from forebrain, cerebellum, brain stem and liver of the three experimental groups (control, sucrose-fed and ethanol-fed) were very similar. However, n-butanol displayed a biphasic action on particulate or soluble preparations of rat forebrain. n-butanol inhibited (competitive inhibition) at higher concentrations (250-500 mM), while at lower concentrations (10-25 mM), the alcohol inhibited at low substrate concentrations but activated at high substrate concentration. These results suggest that the liver is more affected by ethanol than the brain. Moreover, the lipid composition of membranes is probably modified by ethanol or sucrose ingestion and this would affect membrane fluidity and consequently the behaviour of acetylcholinesterase.

Behavior of the cholinergic system in the rat brachial plexus after contralateral neurotomy

Changes in the activity of specific proteins of the cholinergic system were measured in the rat spinal cord (C5 through T1 levels), secondary trunks of the brachial plexus, and extensores carpi muscles of one antimere, at various periods after contralateral transection of the brachial plexus. Choline acetyltransferase (ChAc) specific activity significantly decreased to approximately 50% of the control in all three regions tested within 7 to 16 days; by the 35th day, it had returned to the control values. The behavior of acetylcholinesterase (AChE) specific activity was similar to that for ChAc in nerves and muscles, whereas in the spinal cord it did not display any significant variation. The total (per muscle) activity of the cholinergic receptor (ACh-R) increased to more than 200% of the control muscles, even though its specific activity did not change during the experiment. We suggest that some alteration in the transfer of information between normal and contralateral (axotomized) motoneurons occurs after transection of a peripheral nerve. Several factors could be involved, particularly the interruption of crossed reflex arcs. The neurochemical changes observed may be triggered by a marked decrease in ChAc synthesis in the motoneuron cell body. Whatever the mechanism involved, it appears that some events occurring in the damaged neurons also occur, either wholly or in part, in the contralateral, unimpaired neurons. It also appears that the changes in cholinergic protein activities that develop in muscles after contralateral neurotomy partially mimic those observed after muscular denervation.