Enzymes esterase activity

The pure enzyme was tested for activity against several methylated phenolic and cinnamic acids (Table 2). The enzyme was active on methyl esters of cinnamic acids caffeio p-coumaric> ferulic, and is therefore termed a cinnamoyl esterase (CinnAE). 

The introduction of redox activity through a Co11 center in place of redox-inactive Zn11 can be revealing. Carboxypeptidase B (another Zn enzyme) and its Co-substituted derivative were oxidized by the active-site-selective m-chloroperbenzoic acid.1209 In the Co-substituted oxidized (Co111) enzyme there was a decrease in both the peptidase and the esterase activities, whereas in the zinc enzyme only the peptidase activity decreased. Oxidation of the native enzyme resulted in modification of a methionine residue instead. These studies indicate that the two metal ions impose different structural and functional properties on the active site, leading to differing reactivities of specific amino acid residues. Replacement of zinc(II) in the methyltransferase enzyme MT2-A by cobalt(II) yields an enzyme with enhanced activity, where spectroscopy also indicates coordination by two thiolates and two histidines, supported by EXAFS analysis of the zinc coordination sphere.1210... 

The i-poly(3HB) depolymerase of R. rubrum is the only i-poly(3HB) depolymerase that has been purified [174]. The enzyme consists of one polypeptide of 30-32 kDa and has a pH and temperature optimum of pH 9 and 55 °C, respectively. A specific activity of 4 mmol released 3-hydroxybutyrate/min x mg protein was determined (at 45 °C). The purified enzyme was inactive with denatured poly(3HB) and had no lipase-, protease-, or esterase activity with p-nitro-phenyl fatty acid esters (2-8 carbon atoms). Native poly(3HO) granules were not hydrolyzed by i-poly(3HB) depolymerase, indicating a high substrate specificity similar to extracellular poly(3HB) depolymerases. Recently, the DNA sequence of the i-poly(3HB) depolymerase of R. eutropha was published (AB07612). Surprisingly, the DNA-deduced amino acid sequence (47.3 kDa) did not contain a lipase box fingerprint. A more detailed investigation of the structure and function of bacterial i-poly(HA) depolymerases will be necessary in future. 

By a careful fractionation of normal horse serum, involving as an essential part of the process a separation of closely related substances by the Schtitz168 foam technique, Bader, Schiitz and Stacey16 obtained a crystalline mucoprotein with high choline esterase activity. This appears to be the first mucoprotein obtained without the use of heat or alcohol, and while it is not yet claimed that the crystalline material is indeed the enzyme itself, arguments are advanced to show that the enzymic activity is closely bound up with mucoprotein structure. 

In AChE-based biosensors acetylthiocholine is commonly used as a substrate. The thiocholine produced during the catalytic reaction can be monitored using spectromet-ric, amperometric [44] (Fig. 2.2) or potentiometric methods. The enzyme activity is indirectly proportional to the pesticide concentration. La Rosa et al. [45] used 4-ami-nophenyl acetate as the enzyme substrate for a cholinesterase sensor for pesticide determination. This system allowed the determination of esterase activities via oxidation of the enzymatic product 4-aminophenol rather than the typical thiocholine. Sulfonylureas are reversible inhibitors of acetolactate synthase (ALS). By taking advantage of this inhibition mechanism ALS has been entrapped in photo cured polymer of polyvinyl alcohol bearing styrylpyridinium groups (PVA-SbQ) to prepare an amperometric biosensor for... 

Enzyme activity has been sought in seawater Strickland and Solorzano [288] looked for photomono esterase activity, while Maeda and Taga [289] used a flu-orometric method for assaying deoxyribonuclease activity in both seawater and sediment samples. 

Although hydrolytic enzymes, esterases and amidases, are named after their major substrates, the same enzyme can often hydrolyze esters, thioesters, and amides therefore, the differentiation between esterases and amidases is sometimes artificial. The highest hydrolytic activity is in the liver, but the enzyme pseudocholinesterase is found in the serum. Gut bacteria also contain hydrolytic enzymes. 

Thus a distinction was provided between simple esterases, such as fiver esterase, which catalysed the hydrolysis of simple aliphatic esters but were ineffective towards choline esters. The term 1 cholinesterase was extended to other enzymes, present in blood sera and erythrocytes of other animals, including man, and in nervous tissue, which catalysed the hydrolysis of acetylcholine. It was assumed that only one enzyme was involved until Alles and Hawes2 found that the enzyme present in human erythrocytes readily catalysed the hydrolysis of acetylcholine, but was inactive towards butyrylcholine. Human-serum enzyme, on the other hand, hydrolyses butyrylcholine more rapidly than acetylcholine. The erythrocyte enzyme is sometimes called true cholinesterase, whereas the serum enzyme is sometimes called pseudo-cholinesterase. Stedman,3 however, prefers the names a-cholinesterase for the enzyme more active towards acetylcholine, and / -cholinesterase for the one preferentially hydrolysing butyrylcholine. Enzymes of the first type play a fundamental part in acetylcholine metabolism in vivo. The function of the second type in vivo is obscure. Not everyone agrees with the designation suggested by Stedman. It must also be stressed that enzymes of one type from different species are not always identical in every respect.4 Furthermore,... 

The enzymes used by these workers were cholinesterase, prepared from horse serum, and horse-liver esterase. Parallel experiments were carried out with twice crystallized ovalbumin, and with an aged, dialysed specimen of horse serum with negligible esterase activity. 

We must stress that organo-phosphorus compounds are not specific inhibitors for the cholinesterases, but are rather inhibitors for enzymes possessing carboxylic esterase activity. All the enzymes mentioned below will hydrolyse carboxylic esters. However, not all esterases are inhibited, for example, A-esterase which hydrolyses phenyl acetate is not inhibited by organo-phosphorus compounds. 

Because the metabolism of DEHP was catalyzed by so many fractions of the trout liver homogenate, these fractions were characterized by measurement of marker enzymes to determine which organelles actually were responsible for the observed DEHP metabolism. Succinic dehydrogenase activity was used as a marker for mitochondria, whereas glucose-6-phosphatase was used as a marker for microsomes. The distribution of DEHP oxidase activity (production of polar metabolites 1 and 2 with added NADPH) and of DEHP esterase activity (production of monoester without added NADPH) were also determined. It was found (Figure 2) that the distribution of DEHP oxidase activity parallels the distribution of microsomal activity and the distribution of DEHP esterase activity parallels the distribution of microsomal activity, but is also present in the cytosol fraction. 

Fifth, esterase activity can be due to enzymes with nonesterase main activities. Thus, lysophospholipase (EC 3.1.1.5) and carbonic anhydrase (EC... 

Three isoenzymes of carboxylesterase were purified from rat liver micro-somes and were named RL1, RL2, and RH1. These differ from each other in their response to hormone treatment, inducibility, substrate specificity, and immunological properties [75], It was shown that RL1, RL2, and RH1 resemble hydrolases p/ 6.2/6.4, pI 6.0, and pI 5.6, respectively. Enzyme RL2 was found to be identical to egasyn, a protein with esterase activity found in the endoplasmic reticulum [76], The role of egasyn is to stabilize glucuronidase (EC 3.2.1.31) by noncovalent binding to the microsomal membrane. 

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. 

The intestinal absorption of dietary cholesterol esters occurs only after hydrolysis by sterol esterase steryl-ester acylhydrolase (cholesterol esterase, EC 3.1.1.13) in the presence of taurocholate [113][114], This enzyme is synthesized and secreted by the pancreas. The free cholesterol so produced then diffuses through the lumen to the plasma membrane of the intestinal epithelial cells, where it is re-esterified. The resulting cholesterol esters are then transported into the intestinal lymph [115]. The mechanism of cholesterol reesterification remained unclear until it was shown that cholesterol esterase EC 3.1.1.13 has both bile-salt-independent and bile-salt-dependent cholesterol ester synthetic activities, and that it may catalyze the net synthesis of cholesterol esters under physiological conditions [116-118], It seems that cholesterol esterase can switch between hydrolytic and synthetic activities, controlled by the bile salt and/or proton concentration in the enzyme s microenvironment. Cholesterol esterase is also found in other tissues, e.g., in the liver and testis [119][120], The enzyme is able to catalyze the hydrolysis of acylglycerols and phospholipids at the micellar interface, but also to act as a cholesterol transfer protein in phospholipid vesicles independently of esterase activity [121],... 

Aldehyde dehydrogenase (EC 1.2.1.3) catalyzes the oxidation of aldehydes to acids (see Sect. 3.7.2). The enzyme is ubiquitously distributed, but has mainly been characterized in brain and liver, where it is found in the cytoplasm, mitochondria, and microsomes. It is not clear whether its esterase activity has a physiological role or is a surviving activity inherited from an evolutionary thiolesterase precursor. 

Carbonate anhydrase (carbonic anhydrase, EC 4.2.1.1) catalyzes the reversible interconversion of C02 and HCO3 (see Sect. 3.7.3). The enzyme is found in erythrocytes, and in kidney and gastric juices where it contributes to the control of the acid-base balance. The esterase activity of carbonic anhydrase is probably due to the similarity between its active site and that of the zinc proteases. A possible physiological role of the esterase activity of this enzyme remains to be established. 

Semm albumin is not an enzyme but a transport protein, yet it has demonstrated hydrolytic activity against a variety of xenobiotic substrates. This este-rase-like activity has been known for years, but there is still confusion in the literature regarding its nature and mechanism. Indeed, it was not clear whether this activity is intrinsic to the albumin molecule or results from contamination of albumin preparations by one or more hydrolytic enzymes. More-recent studies with highly purified human serum albumin (HSA) have confirmed that the protein has an intrinsic esterase activity toward several substrates, but that activity due to contaminants and particularly semm cholinesterase is involved... 

F. M. Dickinson, G. W. Haywood, The Effects of Mg2+ on Certain Steps in the Mechanism of the Dehydrogenase and Esterase Reactions Catalysed by Sheep Liver Aldehyde Dehydrogenase. Support for the View That Dehydrogenase and Esterase Activities Occur at the Same Site on the Enzyme , Biochem. J. 1986, 233, 877-883. 

In one case, a small peptide with enzyme-like capability has been claimed. On the basis of model building and conformation studies, the peptide Glu-Phe-Ala-Ala-Glu-Glu-Phe-Ala-Ser-Phe was synthesized in the hope that the carboxyl groups in the center of the model would act like the carboxyl groups in lysozyme 17). The kinetic data in this article come from assays of cell wall lysis of M. lysodeikticus, chitin hydrolysis, and dextran hydrolysis. All of these assays are turbidimetric. Although details of the assay procedures were not given, the final equilibrium positions are apparently different for the reaction catalyzed by lysozyme and the reaction catalyzed by the decapeptide. Similar peptide models for proteases were made on the basis of empirical rules for predicting polypeptide conformations. These materials had no amidase activity and esterase activity only slightly better than that of histidine 59, 60). 

Feruloyl esterase activity was first detected in culture filtrates of Strepto-myces olivochromogenes (49), and has thereafter also been reported for some hemicellulolytic fungi (Table III). A partially purified feruloyl esterase from S. commune liberated hardly any ferulic acid without the presence of xylanase (65). Very recently a feruloyl esterase was purified from Aspergillus oryzae (Tenkanen, M. Schuseil, J. Puls, J. Poutanen, K., /. Biotechnol, in press). The enzyme is an acidic monomeric protein having an isoelectric point of 3.6 and a molecular weight of 30 kDa. It has wide substrate specificity, liberating ferulic, p-coumaric, and acetic acids from steam-extracted wheat straw arabinoxylan. 

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