The catalytic properties and stability of β-galactosidases from fungi

The catalytic activity of β-galactosidases from fungi Penicillium canescens and Aspergillus oryzae is maximum in a weakly acidic medium and does not depend on the presence of magnesium cations in the reaction medium. The enzyme from Aspergillus oryzae fungi is more active, and that from Penicillium canescens is stabler. One of stability indications is the presence of an induction period in the kinetic curves of thermal inactivation. This period disappears at 54°C for the enzyme from Aspergillus oryzae and at 59°C for the enzyme from Penicillium canescens. The temperature dependences of the effective rate constants for the inactivation of the tetrameric enzyme from Penicillium canescens show that the main reason for enzyme inactivation is the dissociation of oligomeric forms below 66°C (E _act = 85 kJ/mol) and enzyme denaturation at higher temperatures (E _act = 480 kJ/mol). The dissociation stage is absent for monomeric β-galactosidase from Aspergillus oryzae fungi, and the activation energy of inactivation is 450 kJ/mol over the whole temperature range studied (53–60°C).     

Effect of magnesium cations on the activity and stability of β-galactosidases

It was shown that the presence of magnesium cations in the reaction mixture increases, approximately twofold, the activity of bacterial Escherichia coli and yeast Kluyveromyces lactis β-galactosidases but does not affect the activity of bovine liver and fungous Penicillium canescens β-galactosidases. The catalytic constants for E. coli and yeast K. lactis β-galactosidases in the presence of 0.01 M and in the absence of Mg²⁺ cations were determined (490 and 220 s^?1 and 59.8 and 37.4 s^?1, respectively). It was shown that the Michaelis constants for these two enzymes are higher in the presence of Mg²⁺ cations, that the thermal stability of E. coli and K. Lactis β-galactosidases is higher in the presence of 0.01 M Mg²⁺, and that the effective rate constants of thermal inactivation of the enzymes are two-to eightfold lower, depending on conditions, in the presence of Mg²⁺ cations. The maximum stabilizing effect of magnesium cations was observed at weak alkaline pH values (7.5–8.5).     

Inhibition of β-galactosidases with mono- and disaccharides

It was demonstrated that, in reactions of the hydrolysis of model substrate 2-nitrophenyl-β-D-galactopyranoside (2-NPGP) monosaccharides D-fructose and D-xylose with hydroxyl substituents oppositely directed at the neighboring carbon atoms in the furan ring, as in D-glucose, act as noncompetitive inhibitors of β-galactosidase from E. coli; for mushroom, β-galactosidases from P. canescens and A. oryzae D-galactose is a stronger inhibitor. It was also found that the inhibition constant is the highest in the case of the most active enzyme (E. coli) and is the lowest for the least active one (P. canescens).     

A comparative study of the structure and properties of β-galactosidases

A comparative study of β-galactosidase amino acid sequences of E. coli and another four out of 11 microorganisms selected at the first stage was performed. It was shown that the functional amino acid residues in the catalytic domain and the ligand environment of the magnesium cation for all five sequences are identical. The mechanism of the catalytic action of E. coli and K. lactis β-galactosidases was investigated by the method of nucleophilic competition. It was shown that the mechanism of the effects of nucleophilic agents is kinetically identical both enzymes: the presence of methanol or butanediols affects the stage of degalactosylation; the presence of magnesium cations promotes the activity of both β-galactosidases; and the mechanisms of the thermal inactivation of E. coli and K. lactis β-galactosidases are different.     

Computational design of a self-assembling β-peptide oligomer

The first computationally designed self-assembling oligomer consisting of exclusively β-amino acids (βAAs) is presented. The packing of a β-3(14) helix into coiled-coils of varying stoichiometries as a function of amino acid sequence is examined. β-Peptides with hVal repeating every third residue in the sequence appeared to have a strong propensity to pack into hexameric bundles. The designed sequence was synthesized and characterized with CD spectroscopy, NMR, and analytical ultracentrifugation, suggesting that the peptide adopts a well-folded hexameric structure.     

Structure and catalytic activity of α-chymotrypsin in solutions of gemini surfactants

The regulatory effect of gemini alkylammonium surfactants (GSurf) with the hexamethylene spacer varying in the length of alkyl radicals on the structure and catalytic activity of a-chymotrypsin was studied. A correlation between the activity of a-chymotrypsin and the length of the alkyl radical of GSurf was found. Gemini surfactants enhance the enzyme activity below the critical micelle concentration (CMC) and inhibit that above the CMC. The results of IR spectroscopy and the data on tryptophan fluorescence show that the interaction of GSurf with a-chymotrypsin induces changes in the protein structure differed in intensity. The most probable enzyme complexes with GSurf were characterized by the molecular docking method.     

Electronic and geometric structure of the protonated forms of nickel β-diketonates

The effect of protonation on the electronic and spatial structure of nickel malonodialdehynate Ni(Mal)₂ and acetylacetonate Ni(Acac)₂ were studied by quantum chemical density functional theory (DFT) method. The metal ring geometry, the energies and the composition of molecular orbitals (MO), the effective charges on atoms, and the total overlap populations were determined, and the possible proton location sites were identified. The variation of the MO energy depending on the electron density distribution on the protonated and non-protonated ligands was considered. Proton addition to one of the oxygen atoms was shown to be most likely.     

Effect of γ-irradiation on the crystallinity and catalytic activity of NdX and NdY zeolites

Different Nd-zeolites were prepared from the original NaX and NaY zeolites by ion exchange. The hydrated and thermally activated (at 550 °C) samples obtained were irradiated with -rays of 1.5 and 10.0 Mrad. The unirradiated and irradiated samples were characterized mainly by X-ray diffraction and tested for catalytic activity in cumene cracking. The X-ray diffraction patterns indicated a slight decrease of crystallinity after irradiation. However, the irradiated samples exhibited higher catalytic activities than unirradiated ones. -Irradiated hydrated zeolites were found to possess comparable activities, whereas the irradiated dehydrated samples were more active. Higher irradiation doses resulted in more active dehydrated zeolites than those irradiated with a lower dose. The observed higher activity was attributed to the formation of tricoordinate aluminium atoms in the zeolite structure, leading to increase of the number of acidic sites and consequently to a catalytic activity.     

Physicochemical properties and catalytic activity of metal–carbon carrier composite materials

Composite metal–carbon materials are created on the basis of different kinds of carbon (multiwall carbon nanotubes, carbon black, Sibunit carbon–carbon material) and metals (Ag, Ni, Co), and their physicochemical and catalytic properties are investigated. It is shown that interaction between metals and carbon carriers proceeds not only with the functional groups on the surfaces of the carriers, but also through a system of–C–C–conjugated bonds. Silver deposited on the surface of a carbon carrier has a crystalline structure (d _cr = 10–15 nm), while nickel has an amorphous lamellar structure. Based on quantum-chemical calculations using the density functional theory, it is shown that cumene oxidation occurs via a homogeneous–heterogeneous mechanism.     

Synthesis and spectroscopic characterization of cobalt porphyrins and their catalytic activity towards dioxygen reduction

The synthesis and spectroscopic characterization of cobalt(Ⅱ) 5-(4-pyridyl)-10,15,20-triphe-nylporphyrin,cobalt(Ⅱ) 5-(4-N-hexadecylpyridiniumyl)-10,15,20-triphenylporphyrin bromide andcobalt(Ⅱ) 5-(2-aminophenyl)-10,15,20-triphenyl-porphyrin are reported.The corresponding copperand vanadyl derivatives ((TriP)Cu,[(hTriP)Cu]~+Br~- and [(hTriP)VO]~+Br~-) were also studied.Eachmetalloporphyrin was characterized by UV-visible,ESR and ~1H NMR spectroscopy.These me-talloporphyrins can be firmly adsorbed on the glassy carbon (GC) surface.The catalytic reduction ofdioxygen at GC electrodes modified by these catalysts was studied by cyclic voltammetry (CV).Thekinetic process of dioxygen reduction at the cobalt porphyrin-modified electrodes was studied with arotating ring disk electrode.     

Strategy to enhance catalytic activity and stability of sol–gel oxidoreductases

Journal of Sol-Gel Science and Technology - Oxidoreductases are widely recognized for their capability to degrade phenolic pollutants and versatile. However, the lack of enzyme stability makes this...     

Complexes of transition metals bonded to silica via β-diketonate groups — synthesis, structure, and catalytic activity

Transition metal complexes bonded to silica via silanes with β-diketonate groups can be used as packings for complexation gas chromatography or as immobilized homogenous metal complex catalysts. On basis of elemental analysis and the determination of surface area, possible structures of the complexes formed on the silica surface have been proposed. The possibility of using the immobilized complexes as catalysts has been indicated. Especially nickel complexes were taken into consideration. These immobilized complexes were used previously as packings for complexation gas chromatography.     

Standard Enthalpies of Formation of β-Aminobutyric Acid and Products of Its Dissociation in Aqueous Solution

Russian Journal of Physical Chemistry A - Heats of dissolution of β-aminobutyric acid in water and aqueous solutions of potassium hydroxide at 298.15 K are measured via direct calorimetry....     

Synthesis and herbicidal activity evaluation of novel β-carboline derivatives

Based on the original structure of harmine, several novel 1,2,3,4-tetrahydro-β-carboline, β-carboline and 1-substituted-β-carboline derivatives bearing a substituted carbohydrazide group at C-3 were designed and synthesized to investigate the structure-activity relationship of their analogues. All of the compounds were characterized by infrared (IR), proton and carbon nuclear magnetic resonance (1H-NMR, 13C-NMR), and mass spectroscopy (MS). The bioassay tests showed that N'-benzylidene-1-phenyl-β-carboline-3-carbohydrazide (C(25)H(18)N(4)O, m.w. 390.4) (c2) and N'-(4-trifluoromethyl-benzylidene)-1-phenyl-β-carboline-3-carbohydrazide (C(26)H(17)N(4)OF(3), m.w. 458) (d2) exhibited good inhibitory activity against dicotyledonous and monocotyledonous weeds, with EC(50) values of 4.83 μM and 14.25 μM, respectively.     

New water-soluble forms of α-tocopherol: preparation and study of antioxidant activity in vitro

Water-soluble forms of α-tocopherol (vitamin E) possessing antioxidant activity in vitro were obtained by encapsulating in N-vinylpyrrolidone with triethylene glycol dimethacrylate polymer particles and were characterized by various physicochemical methods. Quantum-chemical modeling of a structure of α-tocopherol with the copolymer moiety and its theoretical absorption spectra modeling were carried out.     

Preparation and antibacterial activity of aromatic derivatives of β-aminopropionic and γ-aminobutyric acid

Ten aromatic derivatives of β-aminopropionic acid and γ-aminobutyric acid were prepared.Their compositions and structures were identified by elemental analysis,IR,and 1H NMR.They have been examined for their antibacterial action against Staphylococcua aurens and Escherichia coli.These compounds showed higher activity than the aromatic derivatives of ct-amino acid which were reported previously.The general conclusion to be drawn is that the distance between amino and carboxylic group in these molecules could affect their antibacterial activity.Furthermore,those compounds with p-methyl substituent in phenyl ring exhibit higher activity than the others,and all the compounds exhibit higher activity against Escherichia coli and against Staphylococcua aureus.     

Synthesis and characterization of substituted salicylate zirconium compounds and their catalytic activity over ε-caprolactone

In this study, zirconium salicylate compounds (1–6) were prepared by reaction of zirconium(IV) propoxide with 5-chlorosalicylic acid, 4-hydroxysalicylic acid, and 5-nitrosalicylic acid in 1-propanol, respectively. All these compounds (1–6) were characterized by ¹H, ¹³C NMR, FTIR, mass spectroscopy, elemental, and thermogravimetric analyses. These compounds were tested as catalysts in polymerization of ε-caprolactone and were effective. Polycaprolactone was characterized by ¹H, ¹³C NMR, and gel permeation chromatography. The number of salicylate ligands (bonded to zirconium atom) effects and substituents (on salicylate ligands) effects on the polymerization reactions were investigated first time by this study.     

Why does β-secretase zymogen possess catalytic activity? Molecular modeling and molecular dynamics simulation studies

Beta-secretase is a potential target for inhibitory drugs against Alzheimer's disease as it cleaves amyloid precursor protein (APP) to form insoluble amyloid plaques and vascular deposits in the brain. Beta-secretase is matured from its precursor protein, called beta-secretase zymogen, which, different from most of other zymogens, is also partially active in cleaving APP. Hence, it is important to study on the mechanism of the zymogen's activation process. This study was to model the 3-D structure of the zymogen, followed by intensive molecular dynamics (MD) simulations to identify the most probable 3-D model and to study the dynamic structural behavior of the zymogen for understanding the effects of pro-segment on the function of the enzyme. The results revealed that the dropping in catalytic activity of the beta-secretase zymogen could be attributed to the occupation of the entrance of the catalytic site of the zymogen by its pro-segment. On the other hand, the partial catalytic activity of the zymogen could be explained by high fluctuation of the pro-segment in comparison with that of other zymogens, resulting in the occasionally exposure of the catalytic site for access its substrate APP. Indeed, steered MD (SMD) simulation revealed a weak pulling force at quasi-equilibrium state for the pro-segment of the zymogen leaving from the entrance, indicating that this swinging process could take place spontaneously. Furthermore, MM-PBSA calculation revealed a small change of free energy of 10.56 kal/mol between the initial and final states of the process of pro-segment swung outside the binding pocket of beta-secretase zymogen. These results not only account for the partial catalytic activity of beta-secretase zymogen, but also provide useful clues for discovering new potent ligands, as new type of drug leads for curing Alzheimer's disease, to prevent the pro-segment of the zymogen from leaving its catalytic site.     

Synthesis and catalytic activity of rhodium diene complexes bearing indenyl-type fullerene η-ligand

Rhodium η⁵-complexes bearing an indenyl-type fullerene ligand, Rh[C₆₀(PhCH₂)₂Ph](cod) (2), Rh[C₆₀(PhCH₂)₂Ph](nbd) (3) and Rh(C₇₀Ph₃)(cod) (4), have been synthesized from the corresponding fullerene tri-adducts in 93-96% yields. X-ray crystallographic analysis of 4 indicated that the structure of 4 is similar to that of Rh(Ind)(cod). The rhodium complex 2 catalyzes alkyne trimerization reactions and hydroboration reactions.