Non-Specific Esterases

Mandel JS, Berlinger NT, KayN. 1989. Organophosphate exposure inhibits Non-Specific esterase staining in human blood monocytes. Amer J Industrial Med 15 207-212. 

Fig. 7.17 Proposed mechanism for non-specific esterase catalysis involving a serine residue.

Esmolol is an ultra-short-acting relatively 31-selective 3-adrenoceptor antagonist with an elimination half-life of about 9 min. After intravenous administration it is rapidly hydrolysed by non-specific esterases in the blood and tissues to a carboxylic acid metabolite. Following an intravenous infusion its haemodynamic effects are short lasting and disappear within 20-30 min. The main indication in the perioperative period is to treat tachycardia. 

Coumarins also have a C6-C3 skeleton, but they possess an oxygen heterocycle as part of the C3-unit. There are numerous coumarins, many of which play a role in disease and pest resistance, as well as UV-tolerance. The coumarin umbelliferone (1.21) is popular in enzyme assays. Umbelliferone esters can be used as a substrate for non-specific esterase enzyme assays and in fluorescent immunoassays (Jacks and Kircher, 1967). In order to quantify the enzyme activity of the popular reporter gene P-glucuronidase (GUS), plant extracts can be incubated with 4-methylumbelliferyl P-D-glucuronide (4-MUG 1.22), which upon hydrolysis... 

Flydrolysis is an important metabolic reaction for drugs whose structures contain ester and amide groups. All types of ester and amide can be metabolized by this route. Ester hydrolysis is often catalysed by specific esterases in the liver, kidney and other tissues as well as non-specific esterases such as acetylcholinesterases and pseudocholinesterases in the plasma. Amide hydrolysis is also catalysed by non-specific esterases in the plasma as well as amidases in the liver. More specific enzyme systems are able to hydrolyse sulphate and glucur-onate conjugates as well as hydrate epoxides, glycosides and other moieties. 

Studies on non-specific esterases activity in Raillietina tetragona. Helminthologia, 20 45-52. 

The acetoxymethyl ester form of the calcein dye (calcein-AM) has been widely used as an assay to measure viable cells for microscopy, flow cytometry, and some plate-based methods. Calcein-AM is a cell-permeable non-fluorescent compound added to cells as a solution in DMSO. Non-specific esterase activity present in viable cells removes the lipophilic AM group, resulting in conversion of the non-fluorescent calcein-AM into a green fluorescent calcein molecule that is generally retained inside viable cells. 

Pivaloyloxymethyl (Pom) esters are useful as prodrugs of penicillin and other 0-lactam antibiotics owing to their easy hydrolysis in vivo by ubiquitous non-specific esterases. Mascaretti and co-workers showed that Pom esters can also by cleaved under mild conditions with 2 equivalents of bis(tri-/i-butyltin)oxide as shown in Scheme 6.32. The intermediate tributylstannyl esters are readily hydrolysed on treatment with water to release the carboxylic acid. Functional groups such as aldehydes, thioacetals, amides, vinyl bromides, and nitro compounds are compatible.22... 

Enzymes in the mucilage include an invertase (20.) r non-specific esterase ( 2), fi-glucosidase ( 4.), and DNase (21) Evidence suggests that the esterase aids in the erosion of the plant cuticle roles for the other enzymes have not been ascertained. 

Enzymes that hydrolyze lysophospholipids are found in nearly all tissues and organisms. They seem to be non-specific esterases of the serine-histidine type (25) and hardly deserve the name lysophospholipase because they also hydrolyze esters other than phospholipids. They should probably be considered together with such enzymes as cholesterol esterases and monoglyceride lipases as amphiphilic carboxyl ester hydrolases. These non-specific esterases have a preference for amphiphilic (hydrophilic-lipophilic) substrates. Such an enzyme may perhaps hydrolyze lysophospholipis, monoglycerides, diglycerides, and cholesterol esters. 

Fortunately, it is found that acyloxymethyl esters are susceptible to non-specific esterases. These esters contain a second ester group further away from the penicillin nucleus which is more exposed to attack. The products which are formed from hydrolysis are inherently unstable and decompose spontaneously to reveal the free carboxylic acid (Fig. 10.38). 

Fig. 1. Dependence of phospholipase and non-specific esterase activity on substrate concentration. Esterase exhibits Michaelis-Menten kinetics on soluble substrates, whereas a phospholipase becomes fully active above the cmc of the substrate.

Chemical transformations in the liver are greatly facilitated by the action of enzymes within the smooth endoplasmic reticulum of hepatocytes (often called the microsomal fraction). Phase I reactions (oxidation, reduction, and hydrolysis reactions) convert molecules into more polar forms that usually differ in biological activity from the parent form. Oxidation reactions occur primarily under the direction of a family of enzymes called P450- Non-specific esterases in the liver, plasma, and other sites catalyze the hydrolysis of esters, whereas amides are hydrolyzed in the liver. Protein drugs are often degraded by proteases and peptidases, which are abundant in many tissues, including the intestinal tract and plasma. Phase II reactions are conjugation reactions. 

Hydrolysis. Hydrolysis of esters and amides is a common pathway of drug metabolism. The liver microsomes contain non-specific esterases, as do other tissues and plasma. Hydrolysis of an ester results in the formation of an alcohol and an acid hydrolysis of an amide results in the formation of an amine and an acid. The ester procaine, a local anaesthetic, is rapidly hydrolysed by plasma cholinesterases and, to a lesser extent, by hepatic microsomal esterase. An example of an amide which is hydrolysed, is the antiarrhythmic drug procainamide. Enalapril, a prodrug, is hydrolysed by esterases to the active metabolite enalapri-late, which inhibits the angiotensin-converting enzyme. 

Expression of histochemical markers such as non-specific esterase, lysosomal hydrolases and ecto-enzymes. 

The aryloxyphosphoramidates of AZT and ddlT, which contain amide-bound amino acid derivatives and ester-bound aryl alcohols which are cleaved by cellular non-specific esterases, are highly active against HIV in both TK+ and TK" strains. The derivative (3) displays a 50-fold lower ED so than the parent nucleoside whereas the corresponding to(2, 2, 2-trichloroethyl)... 

Masking the chelating carboxylic acid groups with acetoxymethyl (AM) esters, BAPTA and its fluorescent derivatives can be converted to nonpolar compounds that passively cross the plasma membrane. Once in the cell, non-specific esterases cleave the AM ester back to the free indicator and the resulting tetra or penta anion accumulates in the cytosol. Cells incubated in a very dilute dye solution (1-S /aM) still reach a useful concentration of indicator (>2S fiM). This is an extremely valuable technique, especially vfhen used with Ca indicators that exhibit a shift in excitation or emission on ion binding. By these means, researchers can estimate intracellular Ca changes in single cells or populations of cells (8). 

Although the liver is the body s principal centre for metabolic degradation, this process also goes on elsewhere. For example the bloodstream carries non-specific esterases which rapidly hydrolyse almost every kind of ester, natural or fabricated, and they are accompanied by a rather less active nonspecific amidase. Many degradative enzymes operate in the bowel-wall and the kidney. An inactivator of catecholamines, catechol 0-methyltransferase, is found in many tissues, and Section 12.5 describes the enzyme that hydrolyses acetylcholine in the neuromuscular junction. 

Esters of the 3-carboxylic acid group of ampicillin (Section 13.1) are used as pro-drugs, e.g. bacampicillin, talampicillin, and pivampicillin. Their more lipophilic properties ensure better oral absorption. The active drug is liberated by the non-specific esterases of the bloodstream. Esters of erythromycin 4.47)., such as the stearate or ethyl succinate, survive the stomach s acidity, which erythromycin does not, but are hydrolysed back to the true drug in the duodenum. Children, who intensely dislike the bitter taste of chloramphenicol, are given the succinate ester. In both cases, hydrolysis liberates the true drug. 

M. expansa was cytosolic and conjugated CDNB but not bromobenzene or chlorobenzene (Douch and Buchanan 1978). Similarly, glutathione-S-transferase activity in H. contortus was observed only with CDNB as substrate and not with DCNB or l,2-epoxy-3-(p-nitrophenoxy)propane (Kawalek et al. 1984). Neither M. expansa not A. suum produced glucuronides with 4-nitrophenol, 2-aminophenol or 4-methylumbelliferone (Douch and Blair 1975), or possessed measurable DDT-dehydrochlorinase activity (Douch and Buchanan 1978). Various specific (cholinesterase) and non-specific esterases have been detected in trematodes, e.g. using a-naphthyl acetate as substrate, in A laria marcianae (Dickinson and Johnson 1978) and Schistosoma mansoni and Schistosoma haematobium (Coles 1970). 

Nitric oxide donors [sodium nitroprusside, S-nitroso-N-acetyl-D,L-penicillamine or l-hydroxy-2-oxo-3-(N-methyl-6-aminohexyl)-3-methyl-l-triazene = NOC-9] did not affect the activities of non-specific alkaline phosphatase and non-specific esterase in rat and mouse kidney proximal tubulo-cytes which do not contain nitric oxide synthase I (Dahrmann etal. 1997). However, the activities of succinate dehydrogenase (EC 1.3.99.1), cytochrome c oxidase (EC 1.9.3.1), catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), and cholinesterase (EC 3.1.1.7) and different types of adenosine triphosphatase (EC 3.6.1.3) were found reduced. 

Moreover, initial experiments using a standard protocol suggest that the rate of degradation of PHB in vivo is significantly faster than the in vitro hydrolysis rate at the same temperature and pH. The obvious interpretation is that non-specific esterase and lysozyme enzymes secreted by the body s immune system catalyse the process. Indeed it is relatively easy to demonstrate that the polymer is attacked by hog s liver esterase, for example. 

Other evidence against the spherosomal nature and origin of oil bodies comes from studies on the enzymic properties of spherosomes. Several workers have noted that spherosomes from different sources, i.e. from oil-storing and other tissues, contain various hydrolytic enzymes such as acid phosphatases and non-specific esterases, whereas oil-bodies do not (e.g. in Crambe[ l ]) it is possible, of course, that enzymes become lost during development. There is therefore a strong possibility that spherosomes are not the precursors of oil bodies and we are not yet certain about how the latter do arise. 

Commercial vitamin products often contain esters of a-tocopherol (acetate or hydrogen succinate), which are more stable to oxidation compared with free a-tocopherol. However, esterification of the C-6 hydroxyl group (5-33) results in the formation of biologically inactive compounds, but these esters are rapidly hydrolysed to the biologically active a-tocopherol under the action of non-specific esterases. 

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