Phenyl esterase

Phenyl esterase hydrolyzes phenol acid esters (benzoic series) and aliphatic alcohols, such as methyl gallate. 

Lippi et. al (87) and Dirstine (88) circumvented titration by converting the liberated fatty acids into copper salts, which after extraction in chloroform are reacted with diethyldithio-carbamate to form a colored complex which is measured photometrically. While the end point appears to be more sensitive than the pH end point determination, the advantages are outweighed by the additional steps of solvent extraction, centrifugation and incomplete extraction when low concentrations of copper salts are present. Other substrates used for the measurement of lipase activity have been tributyrin ( ), phenyl laurate (90), p-nit ro-pheny1-stearate and 3-naphthyl laurate (91). It has been shown that these substrates are hydrolyzed by esterases and thus lack specificity for lipase. Studies on patients with pancreatitis indicate olive oil emulsion is definitely superior to water soluble esters as substrates for measuring serum lipase activity. 

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. 

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. 

T. M. Kitson, The Action of Cytoplasmic Aldehyde Dehydrogenase on Methyl p-Nitro-phenyl Carbonate and p-Nitrophenyl Dimethylcarbamate , Biochem. J. 1989, 257, 579-584 T. M. Kitson, K. E. Kitson, A Comparison of Nitrophenyl Esters and Lactones as Substrates of Cytosolic Aldehyde Dehydrogenase , Biochem. J. 1996, 316, 225-232 T. M. Kitson, K. E. Kitson, Studies of the Esterase Activity of Cytosolic Aldehyde Dehydrogenase with Resorufin Acetate as Substrate , Biochem. J. 1997, 322, 701-708. 

A few acetates of phenols have been used extensively as probes to investigate esterases, e.g., phenyl acetate (7.15), 4-nitrophenyl acetate (7.16), a-naphthyl acetate (7.17) and 7-acetoxy-4-mc(hyl-27/-[l bcnzopyran-2-onc (4-methylumbelliferyl acetate, 7.18). Such substrates are easy to handle and their phenolic metabolite is readily analyzed, allowing convenient monitoring of the reaction. 

For example, the hydrolysis of phenyl acetate (7.15) by carboxylesterase isozymes was investigated over a broad pH range, allowing many insights into their catalytic mechanisms [30] (see Chapt. 3). This substrate was also used together with various inhibitors to characterize esterases in human and rat tissues [31], Thus, the approximate values of Km (in pM) and Vmax (in pmol min 1 (g tissue)-1) in human tissues were 300 and 60 in liver micro-somes, 200 and 40 in liver cytosol, and 1500 and 250 in plasma, respective-... 

Y. Liao, S. Hendrata, S. Y. Bae, B. Wang, The Effect of Phenyl Substituents on the Release Rates of Esterase-Sensitive Coumarin-Based Prodrugs , Chem. Pharm. Bull. 2000, 48, 1138-1147. 

Phosphinates are a class of organophosphorus compounds, the metabolism of which has received less attention than that of phosphates (see above) or phosphorothioates and P-halidc compounds (see below). Many phosphinates are rapid but transient inhibitors of acetylcholinesterase and carboxyl-esterases. And like organophosphates and phosphonates, phosphinates are substrates of arylesterases (EC 3.1.1.2). This is exemplified by 4-nitrophen-yl ethyl(phenyl)phosphinate (9.62), whose (-)-enantiomer was hydrolyzed by rabbit serum arylesterase almost 10 times faster than the (+)-enantiomer [133],... 

A typical example that illustrates the method concerns the lipase- or esterase-catalyzed hydrolytic kinetic resolution of rac-1-phenyl ethyl acetate, derived from rac-1-phenyl ethanol (20). However, the acetate of any chiral alcohol or the acetamide of any chiral amine can be used. A 1 1 mixture of labeled and non-labeled compounds (S)- C-19 and (f )-19 is prepared, which simulates a racemate. It is used in the actual catalytic hydrolytic kinetic resolution, which affords a mixture of true enantiomers (5)-20 and (J )-20 as well as labeled and non-labeled acetic acid C-21 and 21, respectively, together with non-reacted starting esters 19. At 50% conversion (or at any other point of the kinetic resolution), the ratio of (5)- C-19 to (1 )-19 correlates with the enantiomeric purity of the non-reacted ester, and the ratio of C-21 to 21 reveals the relative amounts of (5)-20 and (J )-20 (98). 

Fig. 6. pH-activity curves for the system eel esterase-phenyl acetates. According... 

Diols can also be selectively monoacylated by treatment with an acylating agent of low reactivity (vinyl, 2,2,2-trifluoroethyl, phenyl, or ethyl esters) in the presence of catalytic amounts of an esterase (Scheme 10.8) [27]. Surprisingly, these enzymatic... 

Dehydrogenation A-Demethylation Hydroxylation Epoxidation Sulfoxidation Oxidations Acetaminophen, benzidine, DES, epinephrine Dimethylaniline, benzphetamine, aminocarb Benzo[a]pyrene, 2-aminofluorene, phenylbutazone 7,8-Dihydrobenzo[a]pyrene Methylphenylsulfide FANFT, ANFT, bilirubin Esterases and Amidases Paraoxon, dimethoate, phenyl acetate Epoxide Hydrolase Benzo(a)pyrene epoxide, styrene oxide DDT-Dehydrochlorinase p,p- DDT Glutathione Reductase Disulfiram... 

E-values (E ) calculated using the equation E = [ln(l-c) (l-ees)]/[ln(l-c) (l + ees)] from data determined by gas chromatographic analysis on a chiral column from samples obtained after esterase-catalyzed hydrolysis of (R,S)-3-phenyl butyric acid ethyl ester [24]. 

Another important research direction is the mimieking of enzymes and the construction of selective catalysts. For these purposes, the polymer is imprinted with the desired reaetion-product or better, a molecule which resembles the transition state of the reaction adducts. If the educts bind specifically to the recognition site, they become confined into these micro-reactors and are supposed to react faster and more defined than outside the cavities [445]. Examples for reactions in the presence of such synthetic enzymes can be found in [452,453,454,455,456,457] (cf Figure 40c). First positive results have been reported, e.g. an synthetic esterase , increasing the rate of alkaline hydrolysis of substituted phenyl-(2-(4-carboxy-phenyl)-acetic esters for 80 times [488] and Diels-Alder catalysis fiuic-tional holes containing titanium lewis-acids [489]... 

FIGURE 57.11. Reaction of a serine esterase with phenyl valerate to yield phenol and valeric acid (Kayyali et al., 1991). 

Perigaud has extended his work on the synthesis and biological activities of phosphotriester derivatives of AZT bearing a phenyl group or L-tyrosinyl residues. The novel AZT-derivatives (21a-d) also incorporating one S-pivaloyl-2-thioethyl residue were obtained via either P(III) or P(V) chemistry from the appropriate aryl precursors and evaluated for their in vitro anti-HIV activity. ECso values for their ability to inhibit HIV-1 replication in various cell culture experiments ranged between micro- and the nanomolar concentrations. S-Pivaloyl-2-thioethyl aryl phosphotriester derivatives of AZT were able to allow the efficient intracellular delivery of the parent nucleotide via their successive intracellular hydrolysis by an esterase and a phosphodiesterase. ... 

Figure 5.6 A diagram showing neuropathy target esterase as a percentage of total esterase activity with phenyl valerate as the substrate.

The esterase got the names neurotoxic esterase or neuropathy target esterase, and the ester phenyl valerate (PV) was found to be a good substrate for this esterase. However, PV is also hydrolyzed by other esterases because paraoxon, which does not give symptoms of delayed neurotoxicity, inhibited the PV activity as much as 80%. The NTE is defined as the hydrolytic activity against PV that is not inhibited by paraoxon but by mipafox. About 3% of the activity is not inhibited by mipafox plus paraoxon. Thus, the part of PV activity due to neurotoxic esterase should be 17%. 

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