Hydrolase acetylcholine

Acetylcholinesterase (EC 3.1.1.7) (AChE) Acetylcholine acetylhydrolase True ChE ChE I ChE Acet-ylthiocholinesterase Acetylcholine hydrolase Acetyl (3-methylcholinesterase Erythrocyte ChE Butyrylcholinesterase (EC 3.1.1.8) (BChE or BuChE) ChE Pseudocholinesterase Plasma ChE Acylcholine acylhydrolase Non-specific ChE ChEII Benzoylcholinesterase Propionylcholinesterase... 

Nimmo lA, Mabood SF. 1979. The nature of the random experimental error encountered when acetylcholine hydrolase and alcohol dehydrogenase are assayed. Anal Biochem... 

There were two clearly separated peaks, C and D, sedimenting at 1.2 M and 1.3 M-sucrose (Fig. 2). Examination by the electron microscope showed them both to have the morphological characteristics of synaptosomes. It is well established that a good enzyme marker for intact synaptosomes is occluded lactic dehydrogenase (L-lactate NAD oxidoreductase, EC 1.1.1.27) (Marchbanks, 1967), a component of the cell sap. As can be seen in Table I, 83 % of the occluded form of the enzyme of the original P2 fraction is shared between peaks C and D. Both also contained succinic dehydrogenase activity owing to the presence of intraterminal mitochondria. The membrane marker acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) was also present in these peaks and was notably absent from the mitochondrial and lysosomal fractions (Table I). 

The cholinesterases, acetylcholinesterase and butyrylcholinesterase, are serine hydrolase enzymes. The biological role of acetylcholinesterase (AChE, EC 3.1.1.7) is to hydrolyze the neurotransmitter acetylcholine (ACh) to acetate and choline (Scheme 6.1). This plays a role in impulse termination of transmissions at cholinergic synapses within the nervous system (Fig. 6.7) [12,13]. Butyrylcholinesterase (BChE, EC 3.1.1.8), on the other hand, has yet not been ascribed a function. It tolerates a large variety of esters and is more active with butyryl and propio-nyl choline than with acetyl choline [14]. Structure-activity relationship studies have shown that different steric restrictions in the acyl pockets of AChE and BChE cause the difference in their specificity with respect to the acyl moiety of the substrate [15]. AChE hydrolyzes ACh at a very high rate. The maximal rate for hydrolysis of ACh and its thio analog acetyl-thiocholine are around 10 M s , approaching the diffusion-controlled limit [16]. 

Neurotoxic venoms of cobras, mambas, and coral snakes Inhibit the enzyme acetylcholinesterase. - This hydrolase normally breaks down the neurotransmitter acetylcholine within nerve synapses. 

One of the most important hydrolases is acetylcholine esterase (cholinesterase). Acetylcholine is a potent neurotransmitter for voluntary muscle. Nerve impulses travel along neurons to the synaptic cleft, where acetylcholine stored in vesicles is released, carrying the impulse across the synapse to the postsynaptic neuron and propagating the nerve impulse. After the nerve impulse moves on, the action of the neurotransmitter molecules must be stopped by cholinesterase, which hydrolyzes acetylcholine to choline and acetic acid. Some dangerous toxins such as the exotoxin of Clostridium botulinum and saxitoxin interfere with cholinesterase, and many nerve agents such as tabun and sarin act by blocking the hydrolytic action of cholinesterase, see also Enzymes Hydrolysis. 

The greatly increased nucleophilicity of the catalytic serine distinguishes it from all other serine residues and makes it an ideal candidate for modification via activity-based probes [58]. Of the electrophilic probe types to profile serine hydrolases, the fluorophosphonate (FP)-based probes are the most extensively used and were first introduced by Cravatt and coworkers [38, 39]. FPs have been well-known inhibitors of serine hydrolases for over 80 years and were first applied as chemical weapons as potent acetylcholine esterase inhibitors. As FPs do not resemble a peptide or ester substrate, they are nonselective towards a particular serine hydrolase, thus allowing the entire family to be profiled. FPs also show minimal cross-reactivity with other classes of hydrolases such as cysteine-, metallo-, and aspartylhydrolases [59]. Furthermore, FP-based probes react only with the active serine hydrolase, and not the inactive zymogen, allowing these probes to interact only with functional species within the proteome [59]. Extensive use of this probe family has demonstrated their remarkable selectivity for serine hydrolases and resulted in the identification of over 100 distinct serine hydrolases... 

Bacillus subtilis /zNB esterase is a member of the a./(3 hydrolase fold family (Moore and Arnold, 1996 Ollis et al., 1992). The canonical a/j3 hydrolase fold consists of a mostly parallel eight-stranded [3 sheet surrounded on both sides by a helices (Nardini and Dijkstra, 1999). p B esterase contains 489 amino acids arranged in a central thirteen-stranded f3 sheet that is surrounded by fifteen a helices (Fig. 12, see color insert). Similar to the structure of acetylcholine esterase (Sussman et al., 1991), a large fraction of the pSB esterase structure has no defined secondary structure (52% random coil, 33% a helix, and 14% /3 sheet). This high degree of random coil structure is allowed in the a/(3 hydrolase fold, where large insertions in loops were found to be tolerated while still maintaining catalytic activity (Nardini and Dijkstra, 1999). 

It is well known that organophosphates, carbamates and sulfonates are acid-transfer-inhibitors of serine hydrolases because they transfer the acid moiety of the inhibitor to the serine hydroxyl of the enzyme active site (34). Extensive evidence indicates that the reaction of these inhibitors with acetylcholinesterases (AChE) appears to involve the same reaction pathway as that for the esters of carboxylic acids, i.e. acetylcholine (see (35) for review), and in fact these inhibitors are considered to be poor substrates of AChE (36), especially the carbamic acid esters ("Equation 30 ). 

Cholinesterases, e.g., acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholi-nesterase (BChE, EC 3.1.1.8), are serine hydrolases that break down the neurotransmitter acetylcholine and other choline esters [5]. In the neurotransmission processes at the neuromuscular junction, the cationic neurotransmitter acetylcholine (ACh) is released from the presynaptic nerve, diffuses across the synapse and binds to the ACh receptor in the postsynaptic nerve (Fig. 1). Acetylcholinesterase is located between the synaptic nerves and functions as the terminator of impulse transmissions by hydrolysis of acetylcholine to acetic acid and choline as shown in Scheme 4. The process is very efficient, and the hydrolysis rate is close to diffusion controlled [6, 7]. 

Cholinesterases (ChEs) are a ubiquitous group of enzymes that hydrolyze esters of choline. A well-known example is acetylcholinesterase (AChE, acetyl choline hydrolase, EC 3.1.1.7), the enzyme responsible for hydrolyzing the important neurotransmitter acetylcholine (ACh). Another ChE is butyrylcholi-nesterase (BuChE, acylcholine acylhydrolase, EC 3.1.1.8), also known as nonspecific cholinesterase. The preferred substrate for AChEs is ACh BuChEs prefer to hydrolyze esters like butyrylcholine and propionylcholine. Both AChE and BuChE are inhibited by some organophosphate (OP) and carbamate (CB) esters and also by other chemicals. 

Serine hydrolases are enzymes that play a key role in diverse physiological systems. They all use a serine side-chain hydroxy group as a nucleophile in their enzymatic reaction. In contrast to the serine proteases of the trypsin/elastase family discussed above, the two esterases discussed here belong to a different mechanistic class that shares no sequence homology or structural similarity. Lipases digest nutritional fat triglycerides and acetylcholinesterase degrades the synaptic neurotransmitter, acetylcholine. 

Since MGL is a serine hydrolase, its sensitivity to many of the available serine hydrolase inhibitors has been explored (Table 3). The results support the hypothesis that MGL can be inhibited by compounds that interact with its reactive serine. On the other hand, the potencies of the inhibitors are quite variable in some cases, this likely reflects differences in assay methodology (i.e., substrate concentration, pH, form of the enzyme). However, in a few cases, the same assay conditions revealed very different inhibitory potencies (e.g., compare the platelet and macrophage membrane studies by Di Marzo et al. 1999). In any event, studies of these compounds are not likely to yield selective inhibitors of MGL. All of these compounds are inhibitors of FAAH (see above) and many are also inhibitors of PLA2, diacylglycerol lipase, and acetylcholine esterase, among other hydrolases. By analogy to the development of the URB series of FAAH inhibitors (Kathuria et al. 2003), it is likely that selective inhibitors of MGL will come from other synthetic avenues. 

Acetylcholinesterase (AchE) hydrolyses the neurotransmitter acetylcholine and yields acetic acid and choline. AchE is a serine hydrolase inhibited by organophosphorus poisons, as well as by carbamates and sulfonyl halides which form a covalent bond to a serine residue in the active site. AchE inhibitors are used in the treatment of various disorders. ... 

Hydrolases Amidohydrolases Esterases Urease Acetylcholine esterase Hydrolysis reactions Urea Acetylcholine NH3, CO2 or H+ H +... 

Neurotransmitters may be determined using the respective hydrolases. Acetylcholine is hydrolyzed by acetylcholinesterase (AChE) according to reaction [VII] ... 

The transfer of acyl groups is commonly encountered in biology, and catalyzed by the acyltransferase family of enzymes. For example, acetylcholinesterase hydrolase hydrolyzes excess acetylcholine after nerve impulses. Many chemical models built to mimic the enzymatic function of acyltransferases have been developed, classically employing cyclodextrins which form hydrophobic complexation intermediates. ... 

The most common approach for determination of OPCs is based on their inhibition of the activity of cholinesterase enzymes (3,4), cholinesterases are hydrolases catalyzing the hydrolysis reaction of a particular choline ester (butyryl-choline, acetylcholine, etc) to the corresponding carboxylic add with the release of choline ... 

An exceptionally reactive serine residue has been identified in a great number of hydrolase enzymes, e. g., trypsin, subtilisin, elastase, acetylcholine esterase and some lipases. These enzymes appear to hydrolyze their substrates by a mechanism analogous to that of chymotrypsin. Hydrolases such as papain, ficin and bromelain, which are distributed in plants, have a cysteine residue instead of an active serine residue in their active sites. Thus, the transient intermediates are thioesters. 

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