4-nitrophenyl Acetate Research Articles

Heavy metal ion inhibition studies of human, sheep and fish α-carbonic anhydrases

Carbonic anhydrases (CAs, EC 4.2.1.1) were purified from sheep kidney (sCA IV), from the liver of the teleost fish Dicentrarchus labrax (dCA) and from human erythrocytes (hCA I and hCA II). The purification procedure consisted of a single step affinity chromatography on Sepharose 4B-tyrosine-sulfanilamide. The kinetic parameters of these enzymes were determined for their esterase activity with 4-nitrophenyl acetate as substrate. The following metal ions, Pb2+, Co2+, Hg2+, Cd2+, Zn2+, Se2+, Cu2+, Al3+ and Mn3+ showed inhibitory effects on these enzymes. The tested metal ions inhibited these CAs competitively in the low milimolar/submillimolar range. The susceptibility to various cations inhibitors differs significantly between these vertebrate α-CAs and is probably due to their binding to His64 or the histidine cluster.

A New Family of Carbohydrate Esterases Is Represented by a GDSL Hydrolase/Acetylxylan Esterase from Geobacillus stearothermophilus

Acetylxylan esterases hydrolyze the ester linkages of acetyl groups at positions 2 and/or 3 of the xylose moieties in xylan and play an important role in enhancing the accessibility of xylanases to the xylan backbone. The hemicellulolytic system of the thermophilic bacterium Geobacillus stearothermophilus T-6 comprises a putative acetylxylan esterase gene, axe2. The gene product belongs to the GDSL hydrolase family and does not share sequence homology with any of the carbohydrate esterases in the CAZy Database. The axe2 gene is induced by xylose, and the purified gene product completely deacetylates xylobiose peracetate (fully acetylated) and hydrolyzes the synthetic substrates 2-naphthyl acetate, 4-nitrophenyl acetate, 4-methylumbelliferyl acetate, and phenyl acetate. The pH profiles for k(cat) and k(cat)/K(m) suggest the existence of two ionizable groups affecting the binding of the substrate to the enzyme. Using NMR spectroscopy, the regioselectivity of Axe2 was directly determined with the aid of one-dimensional selective total correlation spectroscopy. Methyl 2,3,4-tri-O-acetyl-β-d-xylopyranoside was rapidly deacetylated at position 2 or at positions 3 and 4 to give either diacetyl or monoacetyl intermediates, respectively; methyl 2,3,4,6-tetra-O-acetyl-β-d-glucopyranoside was initially deacetylated at position 6. In both cases, the complete hydrolysis of the intermediates occurred at a much slower rate, suggesting that the preferred substrate is the peracetate sugar form. Site-directed mutagenesis of Ser-15, His-194, and Asp-191 resulted in complete inactivation of the enzyme, consistent with their role as the catalytic triad. Overall, our results show that Axe2 is a serine acetylxylan esterase representing a new carbohydrate esterase family.

Palladium-Catalyzed Decarboxylative Coupling of Potassium Nitrophenyl Acetates with Aryl Halides

A palladium-catalyzed decarboxylative cross-coupling of potassium 2- and 4-nitrophenyl acetates with aryl chlorides and bromides has been developed. Because the nitro group can be readily converted to many other functional groups, the new reaction provides a useful method for the preparation of diverse 1,1-diaryl methanes and their derivatives.

Characterization of Recombinant Human Carboxylesterases: Fluorescein Diacetate as a Probe Substrate for Human Carboxylesterase 2

Human carboxylesterase (CES) 1 and CES2 are members of the serine hydrolase superfamily, and both exhibit broad substrate specificity and are involved in xenobiotic and endobiotic metabolism. Although expression of CES1 and CES2 occurs in several organs, their expression in liver and small intestine is predominantly attributed to CES1 and CES2, respectively. We successfully expressed CES1 form b (CES1-b) and form c (CES1-c) as well as CES2 in baculovirus-infected High Five insect cells. With 4-nitrophenyl acetate (4-NPA) as the probe substrate, the K(m) values of recombinant CES1-b and CES2 matched those of human liver microsomes (HLM) and human intestinal microsomes (HIM) with approximately 200 and 180 μM, respectively. Bis(4-nitrophenyl) phosphate potently inhibited 4-NPA hydrolysis by HLM, CES1-b, CES1-c, HIM, and CES2 with IC(50) values less than 1 μM. With fluorescein diacetate (FD) as the substrate, the K(m) values were similar for all enzyme systems, with the exception of CES1-b, which was slightly lower; however, the V(max) values for HIM and CES2 were 39.5 and 14.6 μmol · mg(-1) · min(-1), respectively, which were at least 50-fold higher than those of CES1-b or CES1-c. Loperamide potently inhibited HLM, HIM, and CES2 with similar IC(50) values of approximately 1 μM. Substrate specificity was compared between human tissues and recombinant enzymes. The data suggest the following: 1) FD is a probe substrate for CES2; 2) CES1-b is the predominant form in human liver; and 3) recombinant CES1-b and CES2 expressed in insect cells are functionally consistent with native carboxylesterases expressed in human liver and intestine, respectively.

The effect of lecithin dispersed to surfactants on the hydrolysis of p-nitrophenyl acetate.

The effect of lecithin dispersed to surfactants on the hydrolysis of p-nitrophenyl acetate.

Purification and characterization of carbonic anhydrase from the teleost fish Dicentrarchus labrax (European seabass) liver and toxicological effects of metals on enzyme activity

Carbonic anhydrase (EC 4.2.1.1; CA) was purified and characterized from the liver of the teleost fish Dicentrarchus labrax (European seabass) for the first time. The purification procedure consisted of a single step affinity chromatography on Sepharose 4B-tyrosine-sulfanilamide. The enzyme was purified 78.8-fold with a yield of 46%, and a specific activity of 751.72 U/mg proteins. It has an optimum pH at 7.5; an optimum temperature at 25 °C; an optimum ionic strength at 10 mM and a stable pH at 8.5. The kinetic parameters of this enzyme were determined for its esterase activity, with 4-nitrophenyl acetate (NPA) as substrate and the purified enzyme had an apparent K M and V max values of 0.44 mM and 0.249 μmol x min −1, respectively. The following metals, Al +3, Cu +2, Pb +2, Co +3, Ag +1, Zn +2 and Hg +2 showed inhibitory effects on the enzyme. Al +3 and Cu +2 exhibited the strongest inhibitory action. Pb +2 was moderate inhibitor, whereas other metals showed weaker actions. All tested metals inhibited the enzyme in a competitive manner. Our findings indicate that these metals inhibit the fish enzyme in a similar manner to other α-CAs from mammals investigated earlier, but the susceptibility to various metals differ between the fish and mammalian enzymes. Our results also demonstrate that these metals might be dangerous at low micromolar concentrations for fish CA enzymes.

In Vitro Inhibition of Human Carbonic Anhydrase I and II Isozymes with Natural Phenolic Compounds

Inhibition of two human cytosolic carbonic anhydrase (hCA, EC 4.2.1.1) isozymes I and II with some natural phenolic derivatives was investigated using the esterase assay with 4-nitrophenyl acetate as substrate. Resveratrol, catechin, silymarin, dobutamin, and curcumin showed K(I) values in the range of 4.47-9.47 mm for hCA I and of 2.86-7.44 μm against hCA II, respectively. These natural product phenols were generally competitive inhibitors with 4-nitrophenylacetate as substrate. Some natural phenols investigated here showed effective hCA II inhibitory effects, in the same range as the clinically used sulfonamide acetazolamide, and might be used as leads for generating enzyme inhibitors possibly targeting other CA isoforms that have not been yet assayed for their interactions with such agents.

Characterization and inhibition studies of an α-carbonic anhydrase from the endangered sturgeon species Acipenser gueldenstaedti

An α-carbonic anhydrase (CA, EC 4.2.1.1) was purified and characterized kinetically from erythrocytes of the sturgeon Acipenser gueldenstaedti, an endangered species. The sturgeon enzyme (AgCA) showed kinetic parameters for the CO2 hydration reaction comparable with those of the human erythrocytes enzyme hCA II, being a highly active enzyme, whereas its esterase activity with 4-nitrophenyl acetate as substrate was lower. Sulphonamide inhibitors (acetazolamide, sulphanilamide) strongly inhibited AgCA, whereas metal ions (Ag+, Zn2+, Cu2+ and Co2+) were weak, millimolar inhibitors. Several widely used pesticides (2,4-dichlorophenol, dithiocarbamates, parathion and carbaryl) were also assayed as inhibitors of this enzyme. The dithiocarbamates were low micromolar AgCA inhibitors (IC50 of 16–18 µM), whereas the other pesticides inhibited the enzyme with IC50s in the range of 102–398 µM. The wide use of dithiocarbamate pesticides may be one of the factors enhancing the vulnerability of this sturgeon species to pollutants.

Temperature-sensitive molecularly imprinted microgels with esterase activity

Temperature-sensitive molecularly imprinted microgels (MIGs) exhibiting esterase activity were prepared by a reverse emulsion method using dialdehyde dextran-histidine conjugate (PAD-His) as the functional macromonomer and p -nitrophenyl phosphate (NPP) as the stable transition state analogue (TSA) as well as Co2+ as the coordination center. The catalytic activity of MIGs was greatly influenced by the template amount, and could be modulated by temperature. The hydrolysis kinetics of p -nitrophenyl acetate (NPA) in the presence of MIGs could be described by the Michaelis-Menten equation. The Michaelis-Menten constant and maximium velocity were found to be 2.2×10-5 mol/L and 2.04×10-8 mol/h, respectively. In addition, the MIGs were found to have a high catalytic selectivity to NPA.

Investigating the CO2 uncaging mechanism of nitrophenylacetates by means of fs-IR spectroscopy and quantum chemical calculations

Caged compounds are widely utilized for light-triggered control of biological and chemical reactions. In our study we investigated the photo-induced decarboxylation of all three constitutional isomers of nitrophenylacetate (NPA), which can be regarded as caged-CO(2). UV-pump/IR-probe spectroscopy was used to directly observe the nascent CO(2) in the region of 2340 cm(-1). Together with quantum chemical calculations the reaction models for all three components could be obtained. For meta- and para-NPA the main decarboxylation pathway proceeds via a triplet state with a lifetime of 0.2 ns. In the case of ortho-NPA the photodecarboxylation reaction is suppressed by an H(+)- or H˙-transfer reaction in the excited state as a result of the proximity of the nitro and acetate substituents. Nevertheless, the photodecarboxylation can be investigated due to the isolated spectral position of the CO(2) band. The analysis of the data reveals that a weak ultrafast release channel (<300 fs) represents the main photodecarboxylation reaction pathway for ortho-NPA. The detailed understanding of the molecular mechanisms of CO(2) uncaging should provide general guidelines for the design of systematically improved nitrobenzyl cages.

Characterization and anions inhibition studies of an α-carbonic anhydrase from the teleost fish Dicentrarchus labrax

Carbonic anhydrase (CA; EC 4.2.1.1) was purified from the gill of the teleost fish Dicentrarchus labrax (European seabass). The purification procedure consisted of a single step affinity chromatography on Sepharose 4B-tyrosine-sulfanilamide. The enzyme was purified 84.9-fold with a yield of 58%, and a specific activity of 838.9 U/mg proteins. It has an optimum pH at 8.0; an optimum temperature at 10°C. The kinetic parameters of this enzyme were determined for its esterase activity, with 4-nitrophenyl acetate (NPA) as substrate. The following anions, H₂NSO₃⁻, I⁻, SCN⁻, NO₃⁻, NO₂⁻, N₃⁻, Br⁻, Cl⁻, SO₄²⁻, and F⁻ showed inhibitory effects on the enzyme. Sulfamic acid, iodide, and thiocyanate exhibited the strongest inhibitory action, in the micromolar range (K(i)s of 87-187 μM). NO₃⁻, NO₂⁻ and N₃⁻ were moderate inhibitors, whereas other anions showed only weak actions. All tested anions inhibited the enzyme in a competitive manner. Our findings indicate that these anions inhibit the fish enzyme in a similar manner to other α-CAs from mammals investigated earlier, but the susceptibility to various anions differs significantly between the fish and mammalian CAs.

Carboxy and diphosphate ester hydrolysis promoted by di- or tri-nuclear zinc(II) complexes based on β-cyclodextrin

A new ligand (L), 6-mono-(2-(2-hydroxy-3-(hydroxymethyl)-5-methyl benzylamino)-ethylamino)-β-cyclodextrin, based on β-cyclodextrin derivatives with dinucleating units was synthesized and used to prepare a trimetallic bis-ligands zinc complex (Zn 3(L 2−) 2). The esterase activity of the complex was investigated by the hydrolysis of two carboxylic acid esters, bis(4-nitrophenyl)carbonate (BNPC) and 4-nitrophenyl acetate (NA), and a DNA model bis(4-nitrophenyl)phosphate (BNPP) as a phosphate ester. The catalytic rate for BNPC was very high, which was found to be a 5.63 × 10 3-fold rate enhancement over uncatalyzed hydrolysis and 1.62 × 10 2-fold rate enhancement over uncatalyzed hydrolysis for NA hydrolysis at pH = 7.0. For the catalytic hydrolysis of BNPP, the initial first-order rate constant of 0.1 mM catalyst was 5.85 × 10 −8 s −1 at pH = 8.50 and 35 °C, which is a 731-fold acceleration over uncatalyzed hydrolysis. The second rate constant ( k BNPP) was found to be 1.22 × 10 −3 M −1 s −1 at pH = 10.0. According to the potentiometric titration study, the zinc complex exists in a dinuclear single ligand coordinated mode and a trinuclear bis-ligands system at pH ≥ 7.0. The ester hydrolysis activity was attributed to the cooperative interaction of the two metal centers and the hydrophobic cavity of β-cyclodextrin with substrates.

Ester catalytic hydrolysis by a tridentate N,N′,N″-copper bridged cyclodextrin dimer

Abstract A new pyridine bridged cyclodextrin dimer mono-copper complex (CuL) was synthesized and characterized. The hydrolysis of carboxylic acid esters, bis(4-nitrophenyl)carbonate (BNPC) and 4-nitrophenyl acetate (NA), and phosphate ester, a DNA model bis(4-nitrophenyl)phosphate (BNPP), promoted by CuL has been investigated. The resulting hydrolysis rate constants showed that CuL had a very high rate of catalysis for BNPC hydrolysis, yielding a 2.73 × 103-fold rate enhancement over uncatalyzed hydrolysis at pH 7.00, compared to only a 78.2-fold rate enhancement for NA hydrolysis. The initial first-order rate constant of catalytic hydrolysis for BNPP was 1.01 × 10−7 s−1 at pH 8.5, 35 °C and 0.1 mM catalyst concentration, about 1260-fold acceleration over uncatalyzed hydrolysis. The second rate constant kBNPP of BNPP hydrolysis promoted by CuL was found to be 5.94 × 10−4 M−1 s−1.

Paraoxon, 4-nitrophenyl phosphate and acetate are substrates of α- but not of β-, γ- and ζ-carbonic anhydrases

Carbonic anhydrases (CAs, EC 4.2.1.1) belonging to α-, β-, γ- and ζ-classes and from various organisms, ranging from the bacteria, archaea to eukarya domains, were investigated for their esterase/phosphatase activity with 4-nitrophenyl acetate, 4-nitrophenyl phosphate and paraoxon as substrates. Only α-CAs showed esterase/phosphatase activity, whereas enzymes belonging to the β-, γ- and ζ-classes were completely devoid of such activity. Paraoxon, the metabolite of the organophosphorus insecticide parathione, was a much better substrate for several human/murine α-CA isoforms (CA I, II and XIII), with k cat/ K M in the range of 2681.6–4474.9 M −1 s −1, compared to 4-nitrophenyl phosphate ( k cat/ K M of 14.9–1374.4 M −1 s −1).

Thermodynamics of the Hydrolysis Reactions of 1-Naphthyl Acetate, 4-Nitrophenyl Acetate, and 4-Nitrophenyl α-l-arabinofuranoside

Microcalorimetry, high-performance liquid chromatography (HPLC), and liquid chromatography-mass spectrometry (LC-MS) have been used to conduct a thermodynamic investigation of the hydrolysis reactions {1-naphthyl acetate(aq) + H(2)O(l) = 1-naphthol(aq) + acetate(aq)}, {4-nitrophenyl acetate(aq) + H(2)O(l) = 4-nitrophenol(aq) + acetate(aq)}, and {4-nitrophenyl α-L-arabinofuranoside(aq) + H(2)O(l) = L-arabinose(aq) + 4-nitrophenol(aq)}. Calorimetrically determined enthalpies of reaction Δ(r)H(cal) were measured for all three reactions. However, since the positions of equilibrium for all of these reactions were found to lie very far to the right, it was only possible to set lower limits for the values of the apparent equilibrium constants K'. A chemical equilibrium model, together with pKs and standard enthalpies of reaction Δ(r)H° for the H(+) binding reactions of the reactants and products, was then used to calculate the values of Δ(r)H° for chemical reference reactions that correspond to the overall biochemical reactions that were studied experimentally. The values of Benson estimates of Δ(r)H° for the chemical reference reactions that correspond to the first of the above two reactions were, in all cases, within 16 kJ·mol(-1) of the results obtained in this study. Thermochemical network calculations led to Δ(f)H° = -286.4 kJ·mol(-1) for 1-naphthyl acetate(aq) and Δ(f)H° = -364.9 kJ·mol(-1) for 4-nitrophenyl acetate(aq).

Carbonic Anhydrase Inhibitors: Inhibition of Human Erythrocyte Isozymes I and II with a Series of Phenolic Acids

The inhibitory effects of some phenolic acids on the cytosolic human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes hCA I and hCA II were investigated. Ellagic acid, gallic acid, ferulic acid, caffeic acid, quercetin, p-coumaric acid, p-hydroxybenzoic acid, and syringic acid showed K(I) values in the range of 99-1061 microm for hCA I and of 105-758 microm against hCA II, respectively. Quercetin (for hCA I), p-coumaric acid (for hCA II), and gallic acid (for hCA II) exhibited competitive inhibitory effects with 4-nitrophenyl acetate as substrate. All of the other phenolic acids were found as non-competitive inhibitors with 4-nitrophenylacetate as substrate for hCA I and hCA II. The phenolic acids investigated here showed thus interesting hCA I and hCA II inhibitory effects and might be used as leads for generating enzyme inhibitors possibly targeting other CA isoforms which have not been yet assayed for their interactions with such agents.

Carboxylesterase activity in earthworm gut contents: Potential (eco)toxicological implications

Carboxylesterases (CbEs) are key enzymes in pesticide detoxification. These esterases are involved in the biochemical mechanism for pesticide resistance in some pest species, and further they are considered an efficient protective mechanism against acute toxicity by organophosphate (OP) pesticides in mammals. To gain knowledge on the role of CbEs in pesticide toxicity and natural tolerance in earthworms, we performed an enzyme kinetic analysis to investigate whether these annelids are able to secrete them into their gut lumen. We determined levels of CbE activity and isozyme abundance in the gut wall and ingested soil collected from different portions of the gastrointestinal tract of Lumbricus terrestris. Moreover, modulation of enzyme activity by selected substrates (α-naphthyl acetate [α-NA], 4-nitrophenyl valerate [4-NPV] and 4-nitrophenyl acetate [4-NPA]) and OP pesticides was examined to compare the response between tissue and soil CbEs. We found a high CbE activity in the ingested soil extracts from the crop/gizzard (α-NA-CbE = 8.43 ± 2.76 U mg − 1 protein and 4-NPA-CbE = 5.98 ± 2.11 U mg − 1 protein) compared to the gut wall. Three lines of evidences suggest that the gut epithelium is the main source of this luminal CbE activity. First, the effect of substrate concentrations on CbE activity from both the ingested soil extracts and gut tissues resulted in similar apparent K m and V max values. Second, native PAGE gels revealed that some of the CbE isozymes in the gut tissue were also present in the soil extracts. Third, tissue and soil CbEs showed the same sensitivity to inhibition by OPs. The concentrations of insecticide causing 50% of esterase inhibition (IC 50) was comparable between tissue (IC 50s range = 4.01–9.67 nM dichlorvos and 8480–6880 nM paraoxon) and soil (IC 50s range = 6.01–11.5 nM dichlorvos and 8400–7260 nM paraoxon). Our results suggest a set of (eco)toxicological implications and environmental applications derived from the ability of earthworms to secrete these pesticide-detoxifying enzymes.

Ester Hydrolysis by a Cyclodextrin Dimer Catalyst with a Tridentate N,N′,N′′‐Zinc Linking Group

A new beta-cyclodextrin dimer, 2,6-dimethylpyridine-bridged-bis(6-monoammonio-beta-cyclodextrin) (pyridyl BisCD, L), is synthesized. Its zinc complex (ZnL) is prepared, characterized, and applied as a catalyst for diester hydrolysis. The formation constant (log K(ML)=7.31+/-0.04) of the complex and deprotonation constant (pK(a1)=8.14+/-0.03, pK(a2)=9.24+/-0.01) of the coordinated water molecule were determined by a potentiometric pH titration at (25+/-0.1) degrees C, indicating a tridentate N,N',N''-zinc coordination. Hydrolysis kinetics of carboxylic acid esters were determined with bis(4-nitrophenyl)carbonate (BNPC) and 4-nitrophenyl acetate (NA) as the substrates. The resulting hydrolysis rate constants show that ZnL has a very high rate of catalysis for BNPC hydrolysis, yielding an 8.98x10(3)-fold rate enhancement over uncatalyzed hydrolysis at pH 7.00, compared to only a 71.76-fold rate enhancement for NA hydrolysis. Hydrolysis kinetics of phosphate esters catalyzed by ZnL are also investigated using bis(4-nitrophenyl)phosphate (BNPP) and disodium 4-nitrophenyl phosphate (NPP) as the substrates. The initial first-order rate constant of catalytic hydrolysis for BNPP was 1.29x10(-7) s(-1) at pH 8.5, 35 degrees C and 0.1 mM catalyst concentration, about 1600-fold acceleration over uncatalyzed hydrolysis. The pH dependence of the BNPP cleavage in aqueous buffer was shown as a sigmoidal curve with an inflection point around pH 8.25, which is nearly identical to the pK(a) value of the catalyst from the potentiometric titration. The k(BNPP) of BNPP hydrolysis promoted by ZnL is found to be 1.68x10(-3) M(-1) s(-1), higher than that of NPP, and comparatively higher than those promoted by its other tridentate N,N',N''-zinc analogues.

Different Kinetic Behaviors for Unimolecular and Bimolecular Ester Hydrolysis Reactions in Strongly Acidic Microemulsions

Replacing the counterion in sodium bis(2-ethylhexyl)sulfosuccinate with H(+) allows strongly acidic microemulsions to be obtained. These systems are the only known colloidal medium in which it is possible to reach local concentrations of acid, expressed as Hammett acidity function (H(0)), lower than H(0) = -0.2, which corresponds to a concentration of acid above 1 M in aqueous solution. In the present work, there has been analyzed the influence of this type of microemulsion on the acid hydrolysis of two esters derived from picolinic acid: 4-nitrophenylpicolinate (NPP) and 2,4-dinitrophenylpicolinate (DNPP). The reaction rate for NPP and DNPP increases up to 16 times on increasing the size of the aqueous nanocore of the microemulsion, which supposes an experimental behavior opposed to the one observed for the hydrolysis of nitrophenylacetate (NPA). The key to this differentiated behavior of NPP and DNPP resides in the fact that the rate-determining step for the acid hydrolysis mechanism is the water addition to the protonated ester. The reaction rate increases on increasing the nucleophilicity of water; that is, on increasing W (W = [H(2)O]/[surfactant]). Therefore, the acid hydrolysis of esters in strongly acidic microemulsions presents an A2 mechanism when reactivity increases with W, and an A1 mechanism if it decreases with W.

Effects of head group of cationic surfactants on the hydrolysis of p‐nitrophenyl acetate catalyzed by α‐chymotrypsin

AbstractThe kinetics of hydrolysis of p‐nitrophenyl acetate catalyzed by α‐chymotrypsin (α‐CT) has been studied in the presence of several cationic surfactants having different head groups maintaining the dodecyl hydrophobic residue and bromide counterion. The enzyme activity was tested in the presence of dodecyl trimethylammonium bromide (DTAB), dodecylpyridinium bromide (DPB), dodecyldimethylethanolammonium bromide (DDMEAB), dodecyldiethylethanolammonium bromide (DDEEAB), benzyldimethyldodecylammonium bromide (BDDAB), and dodecyltriphenylphosphonium bromide (DTPB) surfactants. The extent of superactivity depends upon head groups of surfactants. The activity of α‐CT depends on the surfactant concentration and it varies with the surfactant head group dimensions (DTPB &gt; DDEEAB &gt; DTAB &gt; BDDAB &gt; DDMEAB &gt; DPB). For all surfactants, DTPB exhibits highest superactivity. The effects of surfactants on the apparent kinetic parameters like Michaelis constant Km and the catalytic constant kcat have been determined. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 377–381, 2009