Carboxylesterase lipase

Other serine hydrolases such as cholinesterases, carboxylesterases, lipases, and fl-lactamases of classes A, C, and D have a hydrolytic mechanism similar to that of serine peptidases [25-27], The catalytic mechanism also involves an acylation and a deacylation step at a serine residue in the active center (see Fig. 3.3). All serine hydrolases have in common that they are inhibited by covalent attachment of diisopropyl phosphorofluoridate (3.2) to the catalytic serine residue. The catalytic site of esterases and lipases has been less extensively investigated than that of serine peptidases, but much evidence has accumulated that they also contain a catalytic triad composed of serine, histidine, and aspartate or glutamate (Table 3.1). 

Tissue esterases have been divided into two classes the A-type esterases, which are insensitive, and the B-type esterases, which are sensitive to inhibition by organo-phosphorus esters. The A esterases include the arylesterases, whereas the B esterases include cholinesterases of plasma, acetylcholinesterases of erythrocytes and nervous tissue, carboxylesterases, lipases, and so on. The nonspecific arylesterases that hydrolyze short-chain aromatic esters are activated by Ca2+ ions and are responsible for the hydrolysis of certain organophosphate triesters such as paraoxon (Figure 10.10B). 

Tg is one of the largest proteins in the body (molecular weight of the soluble dimer is about 660 kDa, sedimentation coefficient 19 S, isoelectric point 4.4-4.7). It is the major iodoglycoprotein (0.1—2.0% iodine 8—10% total carbohydrate with galactose, mannose, fucose, W-acetyl glucosamine, and sialic acid residues (Venkatesh and Deshpande, 1999)) of the thyroid gland, which consists of two identical subunits (homodimer), and belongs to the type-B carboxylesterase/ lipase family (Park and Arvan, 2004). 

Second, esterases have broad (or even very broad) and overlapping substrate specificities. For example, carboxylesterase (EC 3.1.1.1) also catalyzes reactions characteristic of a number of other hydrolases. The discovery that individual isoenzymes of carboxylesterases may be identical to or closely related to acylglycerol lipase, acylcamitine hydrolase, and palmitoyl-CoA hydrolase (see Sect. 2.4.3) has increased the confusion surrounding esterase classification [59], Many esterases are able to hydrolyze amides, thiolesters,... 

A number of rat liver carboxylesterases identified by their pI values are listed in Table 2.6 [73] five nonspecific carboxylesterases were purified from rat liver and were characterized according to their p/ values [61]. They appeared to be isoenzymes, since they had similar substrate specificities toward phenyl and naphthyl esters and monooleylglycerol. Subsequent studies, however, revealed different specificities with respect to their physiological substrates. The pI 5.2 and 5.6 enzymes were shown to be acylcamitine hydrolases (EC 3.1.1.28), and a p/ 6.0 enzyme an octanoylglycerol lipase. The p/... 

Esterase ESI5 Acylcarnitine hydrolase Carboxylesterase RL2 Esterase pi 5.5 Hydrolase pi 5.6 Acylcarnitine hydrolase Esterase Esterase I Esterase ES10 Carboxylesterase RH1 Octanoylglycerol lipase Esterase pi 6.1 Hydrolase pi 6.2... 

R. Mentlein, H. Rix-Matzen, E. Heymann, Subcellular Localization of Nonspecific Carboxylesterases, Acylcarnitine Hydrolase, Monoacylglycerol Lipase and Palmitoyl-CoA Hydrolase in Rat Liver , Biochim. Biophys. Acta 1988, 964, 319-328. 

It, thus, appears that the capacity to catalyze reactions of transesterification and esterification is a characteristic of various hydrolases (Chapt. 3). Apart from the carboxylesterases discussed here, lipoprotein lipase has the capacity to synthesize fatty acid ethyl esters from ethanol and triglycerides, or even fatty acids [127]. Ethanol, 2-chloroethanol, and other primary alcohols serve to esterify endogenous fatty acids and a number of xenobiotic acids [128-130]. In this context, it is interesting to note that the same human liver carboxylesterase was able to catalyze the hydrolysis of cocaine to benzoylecgonine, the transesterification of cocaine, and the ethyl esterification of fatty acids [131]. 

Carboxylesterase Arylesterase Triacylglycerol lipase Phospholipase A2 Lysophospholipase Acetylesterase Acetylcholinesterase Cholinesterase... 

Lipases are enzymes that hydrolyse triglycerides in fats and phospholipases, as the name indicates, hydrolyse phospholipids. Lipases remove long-chain fatty acids from triglycerides, and they are also frequently described as having esterase activity. There are also specific esterases described in the GI tract, for example, carboxylesterase that is secreted by the pancreas. These enzymes are included in the discussion because their activity may be relevant to the use of macromolecular materials in novel formulations, particularly for oral peptide and nucleic acid delivery. 

Carboxylesterase activity is elevated in mastitic milk and colostrum (Fitz-Gerald et al., 1981) and may correspond to that of the reported lipases from somatic cells (Gaffney and Harper, 1965 Azzara and Dimick, 1985a) and colostrum (Driessen, 1976), respectively. The retinyl esterase activity that co-purifies with, but can be separated from, LPL may also be due to a carboxylesterase (Goldberg et al., 1986). It is of interest that the BSSL in human milk that has been shown to be identical with pancreatic carboxylesterase, has retinyl esterase activity (O Connor and Cleverly, 1989). 

The leucocytes in milk contain a lipase (Gaffney and Harper, 1965 Azzara and Dimick, 1985a) or carboxylesterase (Deeth, 1978), which may contribute to lipolysis in mastitic milk. When suspensions of these cells are added to milk, the level of FFAs increases, almost linearly up to a cell count of ca. 2 x 106/ml (Salih and Anderson, 1978). More lipolysis is observed if the cells are disrupted prior to addition to milk (Jurczak and Sciubisz, 1981). 

Fitz-Gerald, C.H., Deeth, H.C., Kitchen, B.J. 1981. The relationship between the levels of free fatty acids, lipoprotein lipase, carboxylesterase, A-acetyl-p-D-glucosaminidase, somatic cell count and other mastitis indices in bovine milk. J. Dairy Res. 48, 253-265. 

There is little doubt that lipases claimed to be non-regioselective display activity towards the secondary alcoholic mid-position of TAGs, but this may well be different when it comes to re-esterification of that position with fatty acids or their derivatives. Interestingly enough, there is a recent report on conversion of a carboxylesterase into a triacylglycerol lipase by random mutation (Reyes-Duarto et al., 2005). The hydrolytic enzyme was observed to display preference for the sn-2 position of triacylglycerols in an ethanolysis reaction. 

Reyes-Duarto, D., Polaina, J., L6pez-Cortes, N., Alcalde, M., Plou, F. J., Elborough, K., Ballesteros, A., Timmis, K. N., Golyshin, P. N., and Ferrer, M. 2005. Conversion of a carboxylesterase into a triacylglycerol lipase by a random mutation. Angew. Chem., 117,1-5. 

The esterases are involved in the hydrolysis of ester linkages of various types. The products formed are acid and alcohol. These enzymes may hydrolyze triglycerides and include several lipases for instance, phospholipids are hydrolyzed by phospholipases, and cholesterol esters are hydrolyzed by cholesterol esterase. The carboxylesterases are enzymes that hydrolyze triglycerides such as tributyrin. They can be distinguished from lipases because they hydrolyze soluble substrates, whereas lipases only act at the water-lipid interfaces of emulsions. Therefore, any condition that results in increased surface area of the water-lipid interface will increase the activity of the enzyme. This is the reason that lipase activity is much greater in homogenized (not pasteurized) milk than in the non-homogenized product. Most of the lipolytic enzymes are specific for either the acid or the alcohol moiety of the substrate, and, in the case of esters of polyhydric alcohols, there may also be a positional specificity. 

Enzymatic reactions in organic media have been a major issue in the field of biocatalysis over the last two decades. Carboxylesterases (mostly lipases) have been used in monophasic organic solution under controlled values of water activity (ajj for catalyzing ester formation the reaction equilibrium can be shifted towards ester formation by interesterification or transesterification [1]. Direct esterification is often hampered by water formation, which may increase o , thus negatively influencing the equihbrium. 

FAEE Synthase 1,11,111-Ethanol 0-Acyltransferase Carboxylesterase Lipoprotein Lipase -... 

Pancreatic carboxylester lipase, secreted by the pancreas as an active enzyme without proteolytic activation, displays broad substrate specificity and has therefore received many names in the literature carboxylesterase, bile salt-stimulated (or activated or dependent) lipase (due to its absolute requirement for bile salts to hydrolyze insoluble substrates), carboxylester lipase or hydrolase, cholesterol esterase, lysophospholipase, nonspecific lipase, and monoglyceride lipase. The IUPAC classification of the enzyme has been either EC.3.1.1.1 (carboxylester hydrolase) or EC.3.1.1.13 (cholesterolester hydrolase) (Table 2). 

Based on these data, it is concluded that monoterpene esters will undergo in vivo hydrolysis in animals to yield the corresponding alcohols and carboxylic acids. Given that the carboxylesterases and lipases catalysing ester hydrolysis are present in all animals, including fish, it is concluded that monoterpene esters will be hydrolysed to yield monoterpene alcohols and simple aliphatic and aromatic acids. Once hydrolysed, the component alcohols and acids are subject to further oxidative metabolism and/or conjugation. 

Nagayama F, Yasuike T, Ikeru K, Kawamura C (1979) Lipase, carboxylesterase and catechol oxidase of the antartic krill. Trans Tokyo Univ Fish 3 153-159 Nasci C, Fossato VU (1982) Studies on physiology of mussels and their ability in accumulating hydrocarbons and chlorinated hydrocarbons. Environ Technol Lett 3 273-280 Nebert DW, Gelboin HV (1968) Substrate-inducible microsomal aryl hydroxylase in mammalian cell culture. J Biol Chem 243 107-116... 

Lipases a group of carboxylesterases, which preferentially hydrolyse emulsifi neutral fats to fatty acids and glycerol or monoacylglycerols. Calcium ions are required for activity. Pancreatic L. also requires taurocholate. Pancreas and certain plant seeds (e.g. Ricinus) contain particularly high activities of L.In addition, high activities are found in adipose tissue, in the stomach (especially in unweaned infants) and in the liver. Pancreatic L. has M, 35,000. Rapid removal of the third and last fatty acid residue from mixed triacylglycerols is catalysed by a specific mono-acylglycerol lipase (EC 3.1.1.23) produced by the intestinal mucosa. 

Mechanisms of Serine Hydrolases. Typical to enzymatic reactions, the enzyme (E) first binds its substrate (S) at the active site as an enzyme-substrate complex (E S). For the formation of the product P, the enzyme-catalyzed reaction then takes place through the mechanism typical of the enzyme. At the active site of serine hydrolases (lipases, carboxylesterases, and serine proteases), the catalytic machinery is called a cataljdic triad consisting of amino acid residues Ser, His, and either Asp or Glu (Fig. 5). In the E S complex, imidazole of His serves as a general acid/base catalyst, catalyzing the addition of the alcoholic hydroxyl of the serine residue to the carbonyl carbon of the acyl donor (R C02R, the first substrate S ). This leads both to the liberation of the first product P (R OH) and to the formation of the so-called acyl-enzyme intermediate. This ester intermediate then reacts with the second substrate (R OH), which leads to the... 

Chahinian H, Ali YB, AbousaUiam A, Petty S, Mandrich L, Manco G, Canaan S, Sarda L (2005) Substrate specificity and kinetic properties of enzymes belonging to the hormone-sensitive lipase family comparison with non-lipolytic and lipolytic carboxylesterases. Biochim Biophys Acta 1738 29-36... 

Chahinian, H., and L. Sarda. 2009. Distinction between Esterases and Lipases Comparative Biochemical Properties of Sequence-Related Carboxylesterases. Protein Peptide Letters 16 (10) 1149-1161. 

Typical biodegradants abiotic hydrolysis is the most important reaction for initiating the environmental degradation of poly(ethylene terephthalate). Also cutinases and carboxylesterases have both shown the potential to hydrolyze polyester bonds similarly to lipases Donelli, 1 Freddi, G Nie iasz, V A Taddei, Polym. Deg. Stab., 95, 1542-50,2010. 

The enzymatic activity of lipases is very comparable to that of esterases, with the main difference being the chain length and hydrophobicity of the acid moiety of the substrate. Therefore in fine chemical applications, lipases and esterases are being used as alternatives for several conversions. For instance, for the kinetic resolution of 2-arylpropionic acids such as naproxen and ibu-profen, both a lipase and an esterase have been found that can perform a stereoselective hydrolysis yielding the pharmaceutically preferred enantiomer S-naproxen (Bertola et al. 1992 Hedstrom et al. 1993). High activity and ease of production have made the carboxylesterase from Bacillus subtilis Thai 1-8 the prime choice of industry (Quax and Broekhuizen 1994). 

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