Kinetics of inhibition of beta-glucosidase from Ampullarium crossean by bromoacetic acid

Highly Efficient Biotransformation of Phenolic Glycosides Using a Recombinant β-Glucosidase From White Rot Fungus Trametes trogii

Phenolic glycosides are the important bioactive molecules, and their bioavailability can be influenced by enzyme hydrolysis, such as β-glucosidases (EC3.2.1.21) and other glycosyl hydrolases (GHs). Wood rotting fungi possess a superfamily of GHs, but little attention has been paid to the GHs and their potential applications in biotransformation of phenolic glycosides. In this study, two GH3 gene family members of Trametes trogii S0301, mainly expressed in the carbon sources conversion stage were cloned, and TtBgl3 coded by T_trogii_12914 showed β-glucosidase activity toward 4-nitrophenyl β-D-glucopyranoside (pNPG). The recombinant TtBgl3 preferred an intermediately neutral optimum pH with >80% of the maximum activity at pH 5.0-7.0 and was stable at a wide range of pH (5.0-10.0). Phenolic glycosides transformation experiments showed that TtBgl3 was a dual-activity enzyme with both activities of aryl-β-D-glucosidase and β-glucuronidase, and could hydrolyze the β-glucoside/glucuronide bond of phenolic glycosides. Under optimized conditions, the recombinant TtBgl3 had much higher transformation efficiency toward the β-glucoside bond of gastrodin, esculin and daidzin than β-glucuronide bond of baicalin, with the transformation rate of 100 and 50%, respectively. Our homology modeling, molecular docking, and mutational analysis demonstrated that His85 and Lys467 in the acceptor-binding pocket of TtBgl3 were the potential active sites. The point mutation of His85 and Lys467 leads to the significantly impaired catalytic activity toward pNPG and also the weak transformation efficiency toward gastrodin. These findings provide insights for the identification of novel GH3 β-glucosidases from T. trogii and other wood-rotting fungi. Furthermore, TtBgl3 might be applied as green and efficient biological catalysts in the deglycosylation of diverse phenolics to produce bioactive glycosides for drug discovery in the future.

Purification, characterization, and functional groups of an extracellular aflatoxin M1 -detoxifizyme from Bacillus pumilus E-1-1-1

The experiment was conducted to purify high activity extracellular enzymes, which were produced by a strain that we previously screened was able to degrade aflatoxin effectively, and speculate the functional groups of the enzyme associated with degradation. An extracellular aflatoxin-detoxifizyme (DAFE) from Bacillus pumilus E-1-1-1 was purified through a process including ammonium sulfate precipitation, ultrafiltration, Sephadex chromatography, and ion exchange chromatography. The molecular mass of the enzyme assessed by SDS-PAGE was found to be approximately 58 kDa. The optimum reaction temperature and pH for the purified enzyme were 45°C and pH 7, respectively. The enzyme showed temperature stability of up to 60°C. Ba²⁺ , Ca²⁺ Na⁺ , Mn²⁺ , EDTA, and β-mercaptoethanol showed inhibitory effects on the enzyme activity. Mg²⁺ , Fe³⁺ , Zn²⁺ and K⁺ were the activators of enzymes. This enzyme was composed of at least 15 kinds of amino acids. Lysine, tryptophan, and histidine residues were necessary and major functional groups to maintain enzyme activity, disulfide bonds were observed, serine residues had little effect on the enzyme activity, so it was not the necessary group to reflect the enzyme activity, and arginine had no effect on enzyme activity.

Determination of the kinetics and influence of the mercury ion on papain catalytic activity

The effect of the mercury ion on papain activity of the substrate casein and its mechanism were investigated.

Sugarcane bagasse degradation and characterization of three white-rot fungi

In order to investigate the details of lignin biodegradation, the characteristics and process of sugarcane bagasse (SCB) degradation by three lignin degrading fungi, Phanerochaete chrysosporium PC2, Lentinula edode LE16 and Pleurotus ostreatus PO45, were studied. We found that the ligninolytic enzymes polyphenol oxidase (PPO) and manganese peroxidase (MnP) were produced first, and that the cellulolytic enzyme CMCase was produced subsequently. These three fungi were more efficient to degrade lignin (85-93%) than hemicelluloses (64-88%) and cellulose (15-67%) in 12weeks, in which P. chrysosporium PC2 was the most efficient strain to degrade all the ingredients. Results of the FTIR and CP/MAS (13)C NMR revealed that the three fungi preferentially degraded syringyl units. The PPO and MnP as the main ligninolytic enzymes, especially the presence of PPO, were new findings in this study, which improved our knowledge of biopretreatment of SCB and evidenced these strains as valuable resource for SCB biotransformation.

Elucidation of the enantioselective enzymatic hydrolysis of chiral herbicide dichlorprop methyl by chemical modification

Up to 25% of the current pesticides are chiral, the molecules have chiral centers, but most of them are used as racemates. In most cases, enantiomers of chiral pesticides have different fates in the environment. Knowledge of the function of amino acids of enzymes involved in enantioselective behaviors contributes to the understanding of the enantioselectivity of chiral pesticides. In this work, Aspergillus niger lipase (ANL, EC3.1.1.3) was chemically modified using bromoacetic acid (BrAc), 2,3-butanedione (BD), N-bromosuccinimide (NBS), and methanal. The enantioselectivity of the enzymatic hydrolysis of 2,4-dichlorprop-methyl (DCPPM) was investigated by chiral GC. The results have suggested that histidine, arginine, and tryptophan are essential for lipase activity and might be involved in the catalytic site of ANL. In addition, histidine and lysine play an important role in determining the observed enantioselective hydrolysis of chiral herbicide dichlorprop methyl. The molecular modeling study revealed that the essential hydrogen bonds formed between DCPPM and catalytic residues of ANL might be responsible for the enantioselectivity of DCPPM. The loss of enantioselectivity can also arise from the fact that the modification of the amino acids may cause changes in both the nature of the ANL enzyme conformation and the binding pattern of DCPPM. Our study provides basic information for the exploration of the enantioselective interaction mechanism of enzymes with chiral pesticides.

Irreversible competitive inhibitory kinetics of cardol triene on mushroom tyrosinase

Cardol triene was first purified from cashew (Anacardium occidentale L.) nut shell liquid and identified by gas chromatography coupled to mass spectroscopy and nuclear magnetic resonance. The effects of this compound on the activity of mushroom tyrosinase were studied. The results of the kinetic study showed that cardol triene was a potent irreversible competitive inhibitor and the inactivation was of the complexing type. Two molecules of cardol triene could bind to one molecule of tyrosinase and lead to the complete loss of its catalytic activity. The microscopic rate constants were determined for the reaction of cardol triene with the enzyme. The anti-tyrosinase kinetic research of this study provides a comprehensive understanding of inhibitory mechanisms of resorcinolic lipids and is beneficial for the future design of novel tyrosinase inhibitors.

Inhibition kinetics of hydrogen peroxide on β-N-acetyl-d-glucosaminidase from prawn (Penaeus vannamei)

The effects of hydrogen peroxide (H2O2) on prawn NAGase activity for the hydrolysis of pNP-beta-D-GlcNAc have been studied. The results show that H2O2 can reversible inhibit the enzyme (IC50 = 0.85 M) and the inhibition is of a mixed type. The kinetics show that k+o is much larger than k+0, indicating the free enzyme is more susceptible than the enzyme-substrate complex in the H2O2 solution. It is suggested that the presence of the substrate offers marked protection against inhibition by H202. Changes of activity and conformation of the enzyme in different concentrations of H202 have been compared by measuring the fluorescence spectra and residual activity and show that the change of conformation is more rapidly than that of the residual activity, which implies that the whole conformation of the enzyme changes more rapidly than the conformation of the active centre of the enzyme in the H2O2 solution.

Studies on the chemical modification of the essential groups of N-Acetyl-beta-D-glucosaminidase from viscera of green crab (Scylla Serrata)

The chemical modification of N-acetyl-beta-D: -glucosaminidase (EC3.2.1.30) from viscera of green crab (Scylla serrata) has been first studied. The modification of indole groups of tryptophan of the enzyme by N-bromosuccinimide can lead to complete inactivation, accompanying the absorption decreasing at 275 nm and the fluorescence intensity quenching at 338 nm, indicating that tryptophan is essential residue to the enzyme. The modification of histidine residue, the carboxyl groups, and lysine residue inactivates the enzyme completely or incompletely. The results show that imidazole groups of histidine residue or sulfhydryl residues, the carboxyl groups of acidic amino acid, amino groups of lysine residue, and indole groups of tryptophan were essential for the catalytic activity of enzyme, while the results demonstrate that the disulfide bonds and the carbamidine groups of arginine residues are not essential to the enzyme's function.

Inhibitory kinetics of bromacetic acid on beta-N-acetyl-D-glucosaminidase from prawn (Penaeus vannamei)

beta-N-Acetyl-D-glucosaminidase (NAGase, EC.3.2.1.52), a composition of chitinases, cooperates with endo-chitinase and exo-chitinase to disintegrate chitin into N-acetylglucosamine (NAG). NAGase from prawn (Penaeus vannamei) is involved in digestion and molting processes. The investigation of enzymatic properties, functional groups and catalytic mechanism is an essential mission to its commercial application. Bromacetic acid (BrAc) is a specific modifier for the histidine residue in specific condition. In this paper, the effect of BrAc on prawn NAGase activity for the hydrolysis of pNP-NAG has been investigated. The results showed that BrAc can reversibly and non-competitively inhibit the enzyme activity at appropriate concentrations and the value of IC(50) was estimated to be 17.05+/-0.65 mM. The inhibition kinetics of the enzyme by BrAc has been studied using the kinetic method of the substrate reaction. And the inhibition model was set up and the microscopic rate constants for the reaction of the inhibitor with free enzyme and the enzyme-substrate complexes were determined for inactivation and reactivation. The rate constant of the forward inactivation (k(+0)), which is 1.25 x 10(-3)s(-1), is about eight times as much as that of the reverse reactivation (k(-0)), which is 1.64 x 10(-4)s(-1). Therefore, when the BrAc concentration is sufficiently large, the enzyme is completely inactivated.

Purification and characterization of recombinant Escherichia coli-expressed Pichia etchellsii ?-glucosidase II with high hydrolytic activity on sophorose

Beta-glucosidase II (Bgl II), encoded by the betaglu2 gene of the thermo-tolerant yeast Pichia etchellsii, was purified from recombinant Escherichia coli pBG22:JM109. The enzyme had a molecular mass of 176 kDa and was a dimer with an apparent subunit mass of 83 kDa. It exhibited broad substrate specificity and hydrolyzed beta-linked gluco-disaccharides and oligosaccharides, salicin, and cyanogenic glucoside amygladin. The unusually high hydrolytic activity of 7,680 units min(-1) g(-1) protein was obtained on sophorose. Competition experiments performed using differently linked beta-disaccharides indicated these to be hydrolyzed at the same active site. Transglycosylation activity leading to the biosynthesis of several disaccharides and oligosaccharides was observed. The enzyme was placed in glycosyl hydrolase family 3, based on a statistical approach using amino acid composition data. The involvement of His as a catalytically important residue was confirmed by diethylpyrocarbonate modification. Pre-incubation of the purified enzyme with 5 mM p-nitrophenyl-beta-D-glucoside offered 2.5-fold higher residual activity compared with unbound enzyme, indicating protection at the active site. The feasibility of this enzyme as a biocatalyst of choice for the synthesis of glyco-conjugates is discussed.

Unfolding and inactivation of Ampullarium crossean beta-glucosidase during denaturation by guanidine hydrochloride

Changes of activity and conformation of Ampullarium crossean beta-glucosidase in different concentrations of guanidine hydrochloride (GuHCl) have been studied by measuring the fluorescence spectra and its relative activity after denaturation. The fluorescence intensity of the enzyme decreased distinctly with increasing guanidine concentrations, the emission peaks appeared red shifted (from 338.4 to 350.8 nm), whereas a new fluorescence emission peak appeared near 310 nm. Changes in the conformation and catalytic activity of the enzyme were compared. A corresponding rapid decrease in catalytic activity of the enzyme was also observed. The extent of inactivation was greater than that of conformational changes, indicating that the active site of the enzyme is more flexible than the whole enzyme molecule. k(+0)>k(+0)' also showed that the enzyme was protected by substrate to a certain extent during guanidine denaturation.

Inactivation kinetics of mushroom tyrosinase by cetylpyridinium chloride

Cetylpyridinium chloride (CPC) was found to inactivate tyrosinase from mushroom (Agaricus bisporus). CPC can bind to the enzyme molecule and induce the enzyme conformation changes. The fluorescence intensity (at 338.4 nm) of the enzyme decreased distinctly with increasing CPC concentrations, and a new little fluorescence emission peak appeared near 372 nm. The inactivation of the enzyme by CPC had first been studied by using the kinetic method of the substrate reaction described by Tsou. The results showed that the enzyme was inactivated by a complex mechanism that had not been previously identified. The enzyme first quickly binds with CPC reversibly and then undergoes a slow irreversible inactivation. The inactivation reaction is a single molecule reaction and the apparent inactivation rate constant is a saturated trend being independent of CPC concentration if the concentration is sufficiently high. The micro rate constants of inactivation and the association constant were determined.

Microbial beta-glucosidases: cloning, properties, and applications

Beta-glucosidases constitute a major group among glycosylhydrolase enzymes. Out of the 82 families classified under glycosylhydrolase category, these belong to family 1 and family 3 and catalyze the selective cleavage of glucosidic bonds. This function is pivotal in many crucial biological pathways, such as degradation of structural and storage polysaccharides, cellular signaling, oncogenesis, host-pathogen interactions, as well as in a number of biotechnological applications. In recent years, interest in these enzymes has gained momentum owing to their biosynthetic abilities. The enzymes exhibit utility in syntheses of diverse oligosaccharides, glycoconjugates, alkyl- and aminoglucosides. Attempts are being made to understand the structure-function relationship of these versatile biocatalysts. Earlier reviews described the sources and properties of microbial beta-glucosidases, yeast beta-glucosidases, thermostable fungal beta-glucosidase, and the physiological functions, characteristics, and catalytic action of native beta-glucosidases from various plant, animal, and microbial sources. Recent efforts have been directed towards molecular cloning, sequencing, mutagenesis, and crystallography of the enzymes. The aim of the present article is to describe the sources and properties of recombinant beta-glucosidases, their classification schemes based on similarity at the structural and molecular levels, elucidation of structure-function relationships, directed evolution of existing enzymes toward enhanced thermostability, substrate range, biosynthetic properties, and applications.