p-NPA Hydrolysis Research Articles

Carbonic anhydrase encapsulation using bamboo cellulose scaffolds for efficient CO2 capture and conversion

Utilizing carbonic anhydrase (CA) to catalyze CO2 hydration offers a sustainable and potent approach for carbon capture and utilization. To enhance CA's reusability and stability for successful industrial applications, enzyme immobilization is essential. In this study, delignified bamboo cellulose served as a renewable porous scaffold for immobilizing CA through oxidation-induced cellulose aldehydation followed by Schiff base linkage. The catalytic performance of the resulting immobilized CA was evaluated using both p-NPA hydrolysis and CO2 hydration models. Compared to free CA, immobilization onto the bamboo scaffold increased CA's optimal temperature and pH to approximately 45 °C and 9.0, respectively. Post-immobilization, CA activity demonstrated effective retention (>60 %), with larger scaffold sizes (i.e., 8 mm diameter and 5 mm height) positively impacting this aspect, even surpassing the activity of free CA. Furthermore, immobilized CA exhibited sustained reusability and high stability under thermal treatment and pH fluctuation, retaining >80 % activity even after 5 catalytic cycles. When introduced to microalgae culture, the immobilized CA improved biomass production by ∼16 %, accompanied by enhanced synthesis of essential biomolecules in microalgae. Collectively, the facile and green construction of immobilized CA onto bamboo cellulose block demonstrates great potential for the development of various CA-catalyzed CO2 conversion and utilization technologies.

New insight on porcine carboxylesterases expression and activity in lung tissues

Over the course of the last twenty years, there has been a growing recognition of the pig's potential as a valuable model for studying human drug metabolism. This study aimed to investigate the expression, enzymatic activity, inhibitory susceptibility, and cellular localization of carboxylesterases (CES) in porcine lung tissue not yet explored. Our results showed that CESs hydrolysis activity followed Michaelis-Menten kinetics in both cytosolic and microsomal fractions of porcine lung tissues (N = 8), with comparable hydrolysis rates for tested substrates, namely 4-nitrophenyl acetate (pNPA), 4-methylumbelliferyl acetate (4-MUA), and fluorescein diacetate (FD). We also determined the CESs hydrolysis activity in a representative sample of the porcine liver that, as expected, displayed higher activity than the lung ones. The study demonstrated variable levels of enzyme activities and interindividual variability in both porcine lung fractions. Inhibition studies used to assess the CESs' involvement in the hydrolysis of pNPA, 4-MUA, and FD suggested that CESs may be the enzymes primarily involved in the metabolism of ester compounds in the pig lung tissue. Overall, this study provides insight into the distribution and diversity of CES isoforms involved in substrate hydrolysis across different cellular fractions (cytosol and microsomes) in porcine lungs.

Engineering Zinc-Organic Frameworks-Based Artificial Carbonic Anhydrase with Ultrafast Biomimetic Centers for Efficient Hydration Reactions.

Constructing effective and robust biocatalysts with carbonic anhydrase (CA)-mimetic activities offers an alternative and promising pathway for diverse CO2-related catalytic applications. However, there is very limited success has been achieved in controllably synthesizing CA-mimetic biocatalysts. Here, inspired by the 3D coordination environments of CAs, this study reports on the design of an ultrafast ZnN3-OH2 center via tuning the 3D coordination structures and mesoporous defects in a zinc-dipyrazolate framework to serve as new, efficient, and robust CA-mimetic biocatalysts (CABs) to catalyze the hydration reactions. Owing to the structural advantages and high similarity with the active center of natural CAs, the double-walled CAB with mesoporous defects displays superior CA-like reaction kinetics in p-NPA hydrolysis (V0=445.16nMs-1, Vmax=3.83µMs-1, turnover number: 5.97×10-3s-1), which surpasses the by-far-reported metal-organic frameworks-based biocatalysts. This work offers essential guidance in tuning 3D coordination environments in artificial enzymes and proposes a new strategy to create high-performance CA-mimetic biocatalysts for broad applications, such as CO2 hydration/capture, CO2 sensing, and abundant hydrolytic reactions.

Immobilization of carbonic anhydrase in a hydrophobic poly(ionic liquid): A new functional solid for CO2 capture

Poly(ionic liquid)s are interesting materials for CO2 separation due to their affinity towards CO2. Carbonic anhydrase, as an enzyme that catalyzes the hydration reaction of CO2, represents tremendous opportunities for enhanced CO2 capture in aqueous solutions. Yet, when used as a free enzyme solubilized in the liquid medium, it has limited practicality. Here, we report the study on carbonic anhydrase immobilization in poly(ionic liquid)s by entrapment. Due to limited enzyme solubility in the hydrophobic ionic liquid monomer solution, carbonic anhydrase was suspended instead of solubilized prior to bulk polymerization. The immobilization protocol was optimized to maximize the catalytic efficiency of the resulting solid by evaluating the effect of lyophilized suspension hydration and particle size. Immobilized carbonic anhydrase properties were investigated by measurement of kinetic parameters, reusability, thermal and storage stability. Using p-NPA hydrolysis as a model reaction, kinetic parameters were 0.22 s−1 mM−1 (kcat/Km) for free enzyme and 0.06 s−1 mM−1 for the immobilized biocatalyst, indicating a decrease of activity upon immobilization. Immobilized enzyme, however, presented better storage stability than free enzyme as after one month the activity did not change. In the case of dissolved carbonic anhydrase, it decreased by about 30%. The entrapped enzyme could be utilized in 5 consecutive cycles of CO2 hydration while keeping a relative activity superior to 60%.

How hydrophilic group affects drug–protein binding modes: Differences in interaction between sirtuins inhibitors Tenovin-1/Tenovin-6 and human serum albumin

Introduction of hydrophilic groups can improve the solubility of leading drugs but inevitably affect their interaction with proteins. This study selected sirtuin inhibitors Tenovin-1 (T1) and Tenovin-6 (T6) as drug models to determine differences in binding mode to human serum albumin (HSA). T1 and T6 quenched the endogenous fluorescence of HSA via static quenching mechanism. Introduction of hydrophilic groups greatly reduced the binding constant, i.e., from 1.302 × 104 L mol−1 for the HSA-T6 system to 0.128 × 104 L mol−1 for the HSA-T1 system. HSA-T1 system was mainly driven by electrostatic interactions while that of HSA-T6 system was hydrophobic interaction and both systems were spontaneous reactions. Site marker experiments and molecular docking indicated that both systems mainly bound to the hydrophobic site I of HSA. Molecular dynamics (MD) simulation analysis further revealed that Tyr148, Tyr150 and Arg257 residues played a key role in this recognition process for both systems. In particular, T6 maintained additional several hydrogen bonds with the surrounding residues. T1 had almost no effect on the esterase-like activity of HSA, but T6 inhibited the hydrolysis of p-NPA. Furthermore, differential scanning calorimetry (VP-DSC), circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy confirmed that HSA in the T6 system undergone a more significant conformational transition than that in the T1 system.

Carboxylesterases and arylacetamide deacetylase comparison in human A549, H460, and H727 pulmonary cells

AimsHuman carboxylesterases (CESs) and arylacetamide deacetylase (AADAC) are serine-esterase enzymes catalyzing the hydrolysis of many compounds containing esters, amides, thioesters, or acetyl groups. This study aimed to investigate the presence, kinetic parameters, and inhibition of CES1, CES2, and AADAC in A549, H460, and H727 pulmonary cells in both living cells and S9 fractions. Materials and methodsThe p-nitrophenyl acetate (pNPA) and 4-methylumbelliferyl acetate (4-MUA) were used as non-selective esterase substrates, whereas phenacetin as selective AADAC substrate. CESs activities were also investigated in living cells by cellular bioimaging using selective fluorescent probes. Key findingsAADAC gene was detected in A549 and H460 cells; nevertheless, arylesterase activity was not found in relative S9 fractions. Besides, CES1 and CES2 were expressed to a different extent by all lung cells, and enzymatic activities were quite overlapping each other. All enzymes exhibited a typical Michaelis-Menten saturation curve and, regarding 4-MUA, similar Km values were found in both living cells and S9 fractions. Conversely, kinetic parameters relative to the pNPA hydrolysis by S9 fractions were significantly lower than those detected in living cells. Inhibition studies revealed that 4-MUA hydrolysis was inhibited by bis-p-nitrophenyl phosphate and phenylmethanesulfonyl fluoride more than loperamide; on the contrary, pNPA hydrolysis inhibition was limited with similar inhibition profiles being obtained in both living cells and S9 fractions. The presence of carboxylesterases was definitely confirmed by cellular bioimaging. SignificanceThese findings add information to esterase knowledge in pulmonary cells that could be used as in vitro models for toxicological and pharmacological studies.

Activity and Stability of Immobilized Lipase for Utilization in Transesterification of Waste Cooking Oil

Biodiesel is fatty acid methyl ester that commonly derived from vegetable oils and animal fats that can be produced through enzymatic transesterification using lipase. In this study, three different types of lipase were used, which are Lipase Immobilized Pseudomonas cepacia, PcL, Thermomyces lanuginosus, TLIM, and Candida Antarctica A (recombinant from Aspergillus oryzae), CALA. These lipases were compared based on their activity at different pH (6-10), temperature (30-50 °C), activation energy, and amount of lipase loading for hydrolysis of p-NPA into n-NP. The result indicates that among the lipase used in the study, CALA is the preferable biocatalyst in the hydrolysis of p-NPA due to the minimum energy required and higher enzymatic activity at 20 mg of enzyme loading. PcL and CALA used in the study gave the optimum activity at pH 9 except for TLIM at pH 8 and the optimum temperature at 40 °C. The kinetic data obtained for CALA in this reaction were Km = 57.412 mM and Vm = 70 µM/min. This finding shows that CALA is beneficial biocatalysts for the transesterification process to obtain a higher product with lower activation energy. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Structures and esterolytic reactivity of novel binuclear copper(ii) complexes with reduced l-serine Schiff bases as mimic carboxylesterases

Three novel binuclear copper(ii) complexes with reduced l-serine Schiff bases were synthesized and their structures were analyzed with single-crystal X-ray diffraction and DFT calculations. The crystal data revealed that all of these binuclear complexes are chiral. Both 5-halogenated (bromo- and chloro-) binuclear complexes exhibit right-handed helix structural character. Interestingly, the 5-methyl-containing analogue has a two-dimensional pore structure. In this paper, the esterolysis reactivity of the as-prepared complexes shows that in the hydrolysis of p-nitrophenyl acetate (PNPA) these three complexes provide 26, 18, 40-fold rate acceleration as compared to the spontaneous hydrolysis of PNPA at pH 7.0, respectively. Under selected conditions, in excess buffered aqueous solution a rate enhancement by three orders of magnitude was observed for the catalytic hydrolysis of another carboxylic ester, p-nitrophenyl picolinate (PNPP). These complexes efficiently promoted PNPP hydrolysis in a micellar solution of cetyltrimethylammonium bromide (CTAB), giving rise to a rate enhancement in excess of four orders of magnitude, which is approximately 2.0-3.2 times higher than that in the buffer.

Presence and inter-individual variability of carboxylesterases (CES1 and CES2) in human lung

Lungs are pharmacologically active organs and the pulmonary drug metabolism is of interest for inhaled drugs design. Carboxylesterases (CESs) are enzymes catalyzing the hydrolysis of many structurally different ester, amide and carbamate chemicals, including prodrugs. For the first time, the presence, kinetics, inhibition and inter-individual variations of the major liver CES isozymes (CES1 and CES2) were investigated in cytosol and microsomes of human lungs from 20 individuals using 4-nitrophenyl acetate (pNPA), 4-methylumbelliferyl acetate (4-MUA), and fluorescein diacetate (FD) as substrates the rates of hydrolysis (Vmax) for pNPA and 4-MUA, unlike FD, were double in microsomes than in cytosol. In these cellular fractions, the Vmax of pNPA, as CES1 marker, were much greater (30–50-fold) than those of FD, as a specific CES2 marker. Conversely, the Km values were comparable suggesting the involvement of the same enzymes. Inhibition studies revealed that the FD hydrolysis was inhibited by bis-p-nitrophenylphosphate, phenylmethanesulfonyl fluoride, and loperamide (specific for CES2), whereas the pNPA and 4-MUA hydrolysis inhibition was limited. Inhibitors selective for other esterases missed having any effect on above-mentioned activities. In cytosol and microsomes of 20 lung samples, inter-individual variations were found for the hydrolysis of pNPA (2.5–5-fold), FD or 4-MUA (8–15-fold). Similar variations were also observed in CES1 and CES2 gene expression, although determined in a small number (n = 9) of lung samples. The identification of CES1 and CES2 and their variability in human lungs are important for drug metabolism and design of prodrugs which need to be activated in this organ.

Catalytic Activity of Peptide-Nanoparticle Conjugates Regulated by a Conformational Change.

Herein, we present the design and synthesis of a catalytically active peptide-nanoparticle conjugate whose activity is regulated by a defined conformational change in the self-assembled peptide monolayer. A catalytically active peptide, designed after the heterodimeric α-helical coiled-coil principle was immobilized onto gold nanoparticles, and kinetic studies were performed according to the Michaelis-Menten model. The formed peptide monolayer at the gold nanoparticle surface accelerated p-nitrophenylacetate (pNPA) hydrolysis by 1 order of magnitude compared to the soluble peptide while exhibiting no defined secondary structure as determined by infrared (IR) and circular dichroism (CD) spectroscopy. Addition of the complementary peptide-induced coiled-coil formation while significantly hindering the pNPA hydrolysis catalyzed by the peptide-nanoparticle conjugate. The heptad repeat sequence of a coiled-coil opens up the opportunity for regulation of conformation and thus catalytic activity of peptide-nanoparticle conjugates upon interaction with a complementary coiled-coil sequence. Strategies of regulation of catalytic activity by interaction with a complementary cofactor/ligand are well-established in nature and are introduced here into rationally designed peptide-nanoparticle conjugates.

Macrocyclic Zn(II) Complexes: Synthesis, Structure and Hydrolysis of p-Nitrophenyl Acetate (pNPA)

A new series of Zn(II) macrocyclic complexes has been synthesized by the reaction of Schiff bases (derived from dihydrazides and benzil/phthalaldehyde) in the presence of zinc(II) acetate dihydrate in ethanol. The complexes have been characterized by means of elemental and spectral (IR, 1H and 13C NMR) and SEM analysis. The kinetic studies were done to study the catalytic properties of these complexes towards the hydrolysis of p-nitrophenylacetate (pNPA) at 25°C in aqueous dimethylsulphoxide using phosphate buffer (pH = 7.0–8.5). During the reaction, absorbance of p-nitrophenolate increases with increase in time (i.e., increase of p-nitrophenolate concentration) which give information about the reaction progress i.e., ester hydrolysis. On the basis of these results, a plausible mechanism for the hydrolysis of pNPA is proposed. It is observed that coordinated water molecule might be serving as a good nucleophile that effectively catalyzes pNPA hydrolysis. Therefore, this type of complexes can be used as hydrolytic model enzymes.Journal of Institute of Science and Technology, 2015, 20(2): 42-48

Biomimetic Catalytic and Sensing Cascades Built with Two Designer Bolaamphiphilic Self-Assemblies.

A system performing both a catalytic hydrolysis reaction and the direct optical monitoring of the product was created by the combination of two bolaamphiphile self-assemblies. Two bolaamphiphilic self-assemblies were applied as a biomimetic catalyst of p-nitrophenyl acetate (p-NPA) hydrolysis and an optical sensor probe that detects p-NPA hydrolysis through photoluminescence quenching by p-nitrophenol (p-NP), the product of p-NPA hydrolysis. One bolaamphiphilic self-assembly with a histidine moiety catalytically hydrolyzed the p-NPA substrate, and the other self-assembly of tyrosyl bolaamphiphile monitored the product of p-NP by photoluminescence quenching. The progression of the reaction and quenching degree were adjusted by controlling the quantity of histidyl and tyrosyl self-assemblies, respectively. The reaction and subsequent sensing cascade could be interrupted by a reducing agent. The addition of NaBH4 induced the chemical conversion of p-NP to p-aminophenol, which retarded photoluminescence quenching. Thus, it was demonstrated that hydrolysis of an organic substrate and subsequent monitoring of the hydrolysis reaction could be achieved through a combination of independent bolaamphiphilic self-assemblies. This study demonstrated the construction of a catalytic reaction and detection system incorporating designer biomimetic self-assemblies whose functionalities were devised to realize deliberate functions.

Carboxyester hydrolysis promoted by novel nano‐sized macrocyclic Zn(II) complexes

A novel series of nano‐sized Zn(II) macrocyclic complexes has been synthesized using the template method, i.e. by the in situ reaction of Schiff bases (derived from 1,4‐bis(4‐amino‐5‐mercapto‐1,2,4‐triazol‐3‐yl)alkanes/phenylene with salicylaldehyde/2‐hydroxyacetophenone) and 1,4‐dibromobutane in the presence of zinc(II) acetate dihydrate in ethanol. The complexes have been characterized using elemental analysis, infrared and NMR spectroscopies, scanning electron microscopy and thermal analysis. The catalytic properties of these complexes have been investigated kinetically for the hydrolysis of p‐nitrophenylacetate (PNPA) at 25°C in aqueous dimethylsulfoxide using phosphate buffer (pH = 7.0–8.5). During the reaction, absorbance of p‐nitrophenolate increases linearly with time (i.e. increase of p‐nitrophenolate concentration) which indicates that the rate of the reaction increases linearly with time. On the basis of these results, a plausible mechanism for the hydrolysis of PNPA is proposed. It is shown that coordinated water may serve as a good nucleophile that effectively catalyses PNPA hydrolysis. Therefore, these complexes may serve as model compounds for hydrolytic enzymes. Copyright © 2014 John Wiley & Sons, Ltd.

Histidine-functionalized water-soluble nanoparticles for biomimetic nucleophilic/general-base catalysis under acidic conditions

Cross-linking the micelles of 4-dodecyloxybenzyltripropargylammonium bromide by 1,4-diazidobutane-2,3-diol in the presence of azide-functionalized imidazole derivatives yielded surface-cross-linked micelles (SCMs) with imidazole groups on the surface. The resulting water-soluble nanoparticles were found, by fluorescence spectroscopy, to contain hydrophobic binding sites. The imidazole groups promoted the photo-deprotonation of 2-naphthol at pH 6 and catalyzed the hydrolysis of p-nitrophenylacetate (PNPA) in aqueous solution at pH ≥ 4. Although the overall hydrolysis rate slowed down with decreasing solution pH, the catalytic effect of the imidazole became stronger because the reactions catalyzed by unfunctionalized SCMs slowed down much more. The unusual ability of the imidazole–SCMs to catalyze the hydrolysis of PNPA under acidic conditions was attributed to the local hydrophobicity and the positive nature of the SCMs.

Unraveling the Mechanisms of Carboxyl Ester Bond Hydrolysis Catalyzed by a Vanadate Anion

The mechanism of p-nitrophenyl acetate (pNPA) hydrolysis promoted by vanadate ions was investigated utilizing both density functional theory and ab initio methods. In accordance with experiments, suggesting pure hydrolytic ester bond cleavage involving a nucleophilic addition in the rate-limiting transition state, four possible B(AC)2 (acyl-oxygen bond cleavage) mode reaction pathways were modeled. Moreover, two alternative reaction modes were also considered. Geometry optimizations were carried out using B3LYP, BP86, and MPWB1K functionals, conjugated with a 6-31++G(d,p) basis set and a Stuttgart effective core potential (ECP) for the vanadium atom. Single-point calculations were performed utilizing M06, B3LYP-D, and BP86-D functionals as well as B2PLYP-D and MP2 methods with a 6-311++G(2d,2p) basis set (with and without ECP). To address bulk solvation effects, the universal solvation model (SMD) and the conductor-like polarizable continuum model were applied, using the parameters of water. All levels of theory predict the same reaction mechanism, B(AC)2-1, as the lowest-energy pathway on the potential energy surface for pNPA hydrolysis catalyzed by the H(2)VO(4)(-) ion in aqueous media. The B(AC)2-1 pathway passes through two transition states, the first associated with the nucleophilic addition of H(2)VO(4)(-) and the second with the release of p-nitrophenoxide ion (pNP(-)), linked with a tetrahedral intermediate state. The intermediate structure is stabilized via protonation of the acyl oxygen atom by the vanadate and formation of an intramolecular hydrogen bond. The first and second barrier heights are 24.9 and 1.3 kcal/mol respectively, as calculated with the SMD-M06 approach. The theoretically predicted B(AC)2-1 mechanism is in good agreement with the experiment.

Hydrolytic catalysis and structural stabilization in a designed metalloprotein

Metal ions are an important part of many natural proteins, providing structural, catalytic and electron transfer functions. Reproducing these functions in a designed protein is the ultimate challenge to our understanding of them. Here, we present an artificial metallohydrolase, which has been shown by X-ray crystallography to contain two different metal ions – a Zn(II) ion which is important for catalytic activity and a Hg(II) ion which provides structural stability. This metallohydrolase displays catalytic activity that compares well with several characteristic reactions of natural enzymes. It catalyses p-nitrophenyl acetate hydrolysis (pNPA) to within ~100-fold of the efficiency of human carbonic anhydrase (CA)II and is at least 550-fold better than comparable synthetic complexes. Similarly, CO2 hydration occurs with an efficiency within ~500-fold of CAII. While histidine residues in the absence of Zn(II) exhibit pNPA hydrolysis, miniscule apopeptide activity is observed for CO2 hydration. The kinetic and structural analysis of this first de novo designed hydrolytic metalloenzyme uncovers necessary design features for future metalloenzymes containing one or more metals.

Biomimetic Sequestration of CO2 and Reformation to CaCO3 Using Bovine Carbonic Anhydrase Immobilized on SBA-15

The biocatalytic capture of CO2, and its precipitation as CaCO3, over bovine carbonic anhydrase (BCA) immobilized on a pore-expanded SBA-15 support was investigated. SBA-15 was synthesized using TMB as a pore expander, and the resulting porous silica was characterized by XRD, BET, IR, and FE-SEM analysis. BCA was immobilized on SBA-15 through various approaches, including covalent attachment (BCA-CA), adsorption (BCA-ADS), and cross-linked enzyme aggregation (BCA-CLEA). The effects of pH, temperature, storage stability, and reusability on the biocatalytic performance of BCA were characterized by examining para-nitrophenyl acetate (p-NPA) hydrolysis. The Kcat/Km values for p-NPA hydrolysis were 740.05, 660.62, and 680.11 M−1 s−1, respectively, whereas the Kcat/Km value for free BCA was 873.76 M−1 s−1. The amount of CaCO3 precipitate was measured quantitatively using an ion-selective electrode and was found to be 12.41, 11.82, or 11.28 mg CaCO3/mg for BCA-CLEA, BCA-ADS, or BCA-CA, respectively. The present ...

Partially Irreversible Inactivation of Mitochondrial Aldehyde Dehydrogenase by Nitroglycerin

Mitochondrial aldehyde dehydrogenase (ALDH2) may be involved in the biotransformation of glyceryl trinitrate (GTN), and the inactivation of ALDH2 by GTN may contribute to the phenomenon of nitrate tolerance. We studied the GTN-induced inactivation of ALDH2 by UV/visible absorption spectroscopy. Dehydrogenation of acetaldehyde and hydrolysis of p-nitrophenylacetate (p-NPA) were both inhibited by GTN. The rate of inhibition increased with the GTN concentration and decreased with the substrate concentration, indicative of competition between GTN and the substrates. Inactivation of p-NPA hydrolysis was greatly enhanced in the presence of NAD+, and, to a lesser extent, in the presence of NADH. In the presence of dithiothreitol (DTT) inactivation of ALDH2 was much slower. Dihydrolipoic acid (LPA-H2) was less effective than DTT, whereas glutathione, cysteine, and ascorbate did not protect against inactivation. When DTT was added after complete inactivation, dehydrogenase reactivation was quite modest (≤16%). The restored dehydrogenase activity correlated inversely with the GTN concentration but was hardly affected by the concentrations of acetaldehyde or DTT. Partial reactivation of dehydrogenation was also accomplished by LPA-H2 but not by GSH. We conclude that, in addition to the previously documented reversible inhibition by GTN that can be ascribed to the oxidation of the active site thiol, there is an irreversible component to ALDH inactivation. Importantly, ALDH2-catalyzed GTN reduction was partly inactivated by preincubation with GTN, suggesting that the inactivation of GTN reduction is also partly irreversible. These observations are consistent with a significant role for irreversible inactivation of ALDH2 in the development of nitrate tolerance.

N,N-Dimethyl-N-Dodecyl-N-(2-methylbenzimidazoyl) Ammonium Chloride 미셀 용액속에서 p-Nitrophenyl Carboxylic Ester의 가수분해

New functional surfactant, N,N-dimethyl-N-dodecyl-N-(2-methyl benzimidazoyl) ammonium chloride(DDBAC) having benzimidazole(BI) functional group have been synthesized and the critical micellar concentration of DDBAC measured by surface tentiometry and electric conductivity method was <TEX>$8.9{\times}10^{-4}M$</TEX>. Micellar effects in DDBAC functional surfactant solution on the hydrolysis of p-nitrophenylacetate(p-NPA), p-nitro-phenylpropionate(p-NPP) and p-nitrophenylvalerate(p-NPV) were observed with change of various pH (Tris-buffer). The pseudo first rate constants of hydrolysis of p-NPA, p-NPP and p-NPV in optimum concentration of DDBAC solution increase to about 160, 280 and 600 times, respectively, as compared with those of aqueous solution at pH 8.00(Tris-buffer). It is considered that benzimidazole functional moiety accelerates the reaction rates of hydrolysis because they act as nucleophile or general base. In optimum concentration of DDBAC solution, the rate constants of hydrolysis of p-NPP and p-NPV increase to about 1.5 and 3.0 times, respectively, as compared with that of p-NPA. It means that the more the carbon numbers of alkyl group of substrates, the larger the binding constants between DDBAC micelle and substrates are. To know the hydrolysis mechanism of p-NPCE(p-NPA, p-NPP and p-NPV), the deuterium kinetic isotope effects were measured in <TEX>$D_2O$</TEX> solutions. Consequently the pseudo first order rate constant ratios in <TEX>$H_2O$</TEX> and <TEX>$D_2O$</TEX> solution, <TEX>$k_{H_2O}/k_{D_2O}$</TEX>, were about <TEX>$2.8{\sim}3.0$</TEX> range. It means that the mechanism of hydrolysis were proceeded by nucleophile and general base attack in approximately same value.

Esterase Inhibition by Grapefruit Juice Flavonoids Leading to a New Drug Interaction

Our previous studies described a newly identified potential of grapefruit juice (GFJ) in mediating pharmacokinetic drug interactions due to its capability of esterase inhibition. The current study identifies the active components in GFJ responsible for its esterase-inhibitory effect. The esterase-inhibitory potential of 10 constitutive flavonoids and furanocoumarins toward p-nitrophenylacetate (PNPA) hydrolysis was investigated. The furanocoumarins bergamottin, 6',7'-dihydroxybergamottin, and bergapten, and the glycoside flavonoids naringin and hesperidin, at concentrations found in GFJ or higher, did not inhibit the hydrolysis of PNPA by purified porcine esterase and human liver microsomes. However, the flavonoid aglycones morin, galangin, kaempferol, quercetin, and naringenin showed appreciable inhibition of PNPA hydrolysis in purified porcine esterase, and human and rat liver systems. In Caco-2 cells, demonstrated to contain minimal CYP3A activity, the permeability coefficient of the prodrugs lovastatin and enalapril was increased in the presence of the active flavonoids kaempferol and naringenin, consistent with inhibition of esterase activity. In rats, oral coadministration of kaempferol and naringenin with these prodrugs led to significant increases in plasma exposure to the active acids. In addition, in portal vein-cannulated rats, coadministration of lovastatin with kaempferol (10 mg/kg) led to a 154% and a 113% increase in the portal plasma exposure to the prodrug and active acid, respectively, compared with coadministration with water. The contribution of CYP3A inhibition was demonstrated to be minimal. Overall, a series of flavonoids present in GFJ are identified as esterase inhibitors, of which kaempferol and naringenin are shown to mediate pharmacokinetic drug interaction with the prodrugs lovastatin and enalapril due to their capability of esterase inhibition.