Acyl-hydrolase

In contrast to acetylcholinesterase, cholinesterase (acylcholine acyl-hydrolase, butyrylcholinesterase, EC 3.1.1.8) exhibits relatively unspecific esterase activity toward choline esters, with abroad specificity relative to the size of the acyl group. The enzyme is synthesized in the liver and can be found in smooth muscle, adipocytes, and plasma. Its physiological role remains partly obscure, but there is evidence that it is present transiently in the embryonic nervous system, where it is replaced in later stages of development by acetylcholinesterase. It has, therefore, been suggested that cholinesterase functions as an embryonic acetylcholinesterase. 

PHOSPHOLIPASE A2 Phosphatidylcholine 2-acyl hydrolase, PHOSPHOLIPASE A2 Phosphatidylcholine, hydrolysis of, PHOSPHOLIPASE A2 PHOSPHOLIPASE D... 

Table I. Microorganisms Producing Tannase (tannin-acyl hydrolase)...

Lipases (triacyl glycerol acyl hydrolases, E.C 3.1.1.3) are a unique class of hydrolases for asymmetric synthesis86,87,S9,90e, They are available from fungi, bacteria and mammalians. The lipases most commonly used so far are the commercially supplied pig pancreas lipase (PPL)136, Pseudomonas cepacia lipase (PCL)89,137 and Candida cylindracea lipase (CCL). In most cases only the crude lipases, consisting of a mixture of proteins which may even be other hydrolases, are successfully applied1373. 

Rydel, T. J., Williams, J. M.,Krieger, E.,Moshiri, F., Stallings, W. C., Brown, S. M., Pershing, J. C.,Purcell, J. P., Alibhai, M. F. (2003). The crystal structure, mutagenesis, and aetivity studies reveal that patatin is a lipid acyl hydrolase with a Ser-Asp catalytie dyad. Biochemistry, 42, 6696-6708. 

Succinylcholine is a neuromuscular blocking agent, which is used clinically to cause muscle relaxation. Its duration of action is short due to rapid metabolism—hydrolysis by cholinesterases (pseudocholinesterase or acylcholine acyl hydrolase)—in the plasma and liver to yield inactive products (Fig. 7.55). Thus, the pharmacological action is terminated by the metabolism. However, in some patients, the effect is excessive, with prolonged muscle relaxation and apnea lasting as long as two hours compared with the normal duration of a few minutes. 

Lipases (triacylglycerol acyl hydrolases, EC 3.1.1.3), have been well established as a valuable catalyst in organic synthesis.12 They are usually distinguished from carboxyl esterases (EC 3.1.1.1) by their substrate spectra, i.e. esterases prefer water soluble substrates and lipases show significantly higher activity towards their natural substrates,... 

The patatin family consists of various glycoproteins in plants making up more than 40% of the total soluble protein in potato tubers. Patatins serve as storage proteins and it has been demonstrated that they exhibit both lipid acyl hydrolase and acetyl transferase activities, which might be involved in tissue wounding responses. Further, recent studies report on antioxidant activities of the major potato allergen Sola t 1 (Seppala et al. 2000). 

Arachidonic acid, a 20-carbon fatty acid, is the primary precursor of the prostaglandins and related compounds (see Figure 39.3). Arachidonic acid is present as a component of the phospholipids of cell membranes, primarily phosphatidyl inositol and other complex lipids.1 Free arachidonic acid is released from tissue phospholipids by the action of phospholipase A2 and other acyl hydrolases, via a process controlled by hormones and other stimuli (see Figure 39.3). There are two major pathways in the synthesis of the eicosanoids from arachidonic acid (see Figure 39.3). 

Stahl, U., Banas, A., and Stymne, S. 1995. Plant microsomal phospholipid acyl hydrolases have selectivities for uncommon fatty acids. Plant Physiol., 107, 953-962. 

Fig. 1. Biosynthetic pathway of C6 and Cg-compounds from Ci8"fatty acids. LAH, Lipolytic Acyl Hydrolase ADH, Alcohol Dehydrogenase IF, Isomerization Factor.

The mechanism by which xenobiotic alcohols or esters are converted to fatty acid esters has not been studied. They could be formed by the action of lyase enzymes in the presence of fatty acid glyceryl esters, as in the conversion of farnesol to farnesol fatty acid esters (150). Some lipolytic acyl hydrolase enzymes from plants readily catalyze the transfer of lipid-bound fatty acids to low MW alcohol acceptors (150.151) and enzymes of this class could be responsible for the occasional formation of fatty acid conjugates of xenobiotic alcohols. Mechanisms involving fatty acid acyl CoA, phospholipids, or direct esterification with fatty acids might also be involved (1 ). 

Early studies with purified ricin demonstrated calcium-independent phospholipase type A and A2 activity, as well as nonspecific acyl hydrolase lysophospholipase type A and A2 activity... 

Lipases (triacyl glycerol acyl hydrolases, E.C. 3.1.1.3) are a unique class of hydrolases i113-115 for asymmetric synthesis based on prochiral or racemic substrates. The application of lipases as biocatalysts has been reviewed emphasizing different... 

The classification of the phospholipases, based on their site of attack, is given in Fig. 2. The phospholipases A (PLAs) are acyl hydrolases classified according to their hydrolysis of the 1-acyl ester (PLA,) or the 2-acyl ester (PLA2). Some phospholipases will hydrolyze both acyl groups and are called phospholipase B (PLB). In addition, lysophospholipases... 

The phospholipases A, (PLAjS) comprise a large group of 1-acyl hydrolases, some of which also degrade neutral lipids (lipases) or remove the acyl group at position 2 in addition to that at position 1 (PLB), and thus must have lysophospholipase activity. Where the enzyme appears to show low selectivity for the sn-l or sn-2 position, the term phospholipase A is used. The term phospholipase B should be restricted to those enzymes where the mechanism involves minimal accumulation of lysophospholipid product. In this section, we consider various enzymes of the PLA type that do not fit a more precise definition in terms of acyl chain selectivity. 

Species relatiouships for plasma acylchohue-acyl hydrolase usiug three differeut... 

This enzyme (triacylglycerol acyl-hydrolase) has a molecular mass of approximately 42 kDa (Hide, Chan, and Li 1992) and a short half-life of about 1-3 h in dogs. Pancreatic lipase is secreted in its active form, and this activity is enhanced by colipase and bile salts the enzyme hydrolyzes triglycerides to monoglycerides. Other lipases— phospholipase a, phospholipase b, and cholesterol ester hydrolase—are also secreted by the pancreas. 

Dhondt, S., G. Gouzerh, A. Muller, M. Legrand, and T. Heitz. 2002. Spatio-temporal expression of patatin-like lipid acyl hydrolases and accumulation of jasmonates in elicitor-treated tobacco leaves are not affected by endogenous levels of salicylic acid. Plant J. 32 749-762. 

The following experiments illustrate that when studying the involvement of phospholipase in the host-pathogen interaction, the total contribution of enzyme of host origin may be considerably higher than previously realized. Rodionov and Zakharova (32) recently reported very high rates of autolytic hydrolysis of membrane lipids in homogenates of potato leaves (26-37% of the phospholipids were hydrolyzed after 2 h at 0-1 ). Our laboratory recently confirmed this observation and proceeded to study sosie of the properties of the lipolytic acyl hydrolase activity in potato leaves (6). Lipolytic acyl hydrolase activity is apparently inactivated by polyphenol oxidase or its toxic quinone products. 

Lumen et al. (17) beans possess a very liigh lipoxygenase activity. We therefore investigated the formation of Cg-components from linolenic acid in homogenates of Beans. The volatiles were determined according to Tressl and Drawert 2). it can be seen that linoleic acid and methyl linolenate are converted into (Z)-3-hexenal, ( E)-2-hexenal, and (E)-2-hexenol. Beans possess a very active fatty acid acyl hydrolase activity (Eq). During 1 min homogenization 100 mg methyl linolenate were hydrolized. As shown by Lumen et al. 

The breakdown of triacylglycerol is catalysed by lipases. A large number of such enzymes have been purified from animals, plants and microbes (cf. Brockerhoff and Jensen, 1974). It should be noted that the term lipase is frequently misused. A true lipase is one which attacks triacylglycerols and acts only at an oil-water interface. This definition therefore excludes enzymes acting on water-soluble esters (esterases) or those preferentially hydrolysing other lipids (acyl hydrolases). 

Although bacteria do not store energy as triacylglycerol, a number of bacterial lipases have been discovered and studied. An extensive review of microbial lipases (and esterases) has been made by Lawrence (1967). It should be emphasized also that many of the microbial Upases (e.g. the widely studied Rhizopus arrhizus enzyme) are, in fact, acyl hydrolases. 

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