Coimmobilization of urease and glutamate dehydrogenase in electrochemically prepared polypyrrole-polyvinyl sulfonate films

Immobilization of urease and glutamate dehydrogenase enzymes in electrochemically prepared polypyrrole-polyvinyl sulfonate films (PPY-PVS) was carried out using physical adsorption and electrochemical entrapment techniques. Detailed studies on optimum pH, Fourier transform infrared spectroscopy, cyclic voltammetry, and scanning electron microscopy of the enzymes in the immobilized state were conducted. The value of the apparent Michaelis-Menten constant was experimentally determined to be 2.5 and 2.7 for physically adsorbed and electrochemically entrapped urease in PPY-PVS films, respectively.     

Site-directed mutagenesis study on the thermal stability of a chemiric PQQ glucose dehydrogenase and its structural interpretation

We have previously reported that a chimeric pyrroloquinoline quinone (PQQ) glucose dehydrogenase (GDH), E97A3, which was made up of 97% of Escherichia coli PQQGDH sequence and 3% of Acinetobacter calcoaceticus PQQGDH, showed increased thermal stability compared with both parental enzymes. Site-directed mutagenesis studies were carried out in order to investigate the role of amino-acid substitution at the C-terminal region, Ser 771, of a chimeric PQQGDHs on their thermal stability. A series of Ser 771 substitutions of a chimeric PQQGDH, E99A1, confirmed that hydrophobic interaction governs the thermal stability of the chimeric enzymes. Comparison of the thermal denaturation of E. coli PQQGDH and E97A3 followed by far-ultraviolet (UV) circular dichroism (CD) spectroscopy revealed that E97 A3 acquired stability at the first step of denaturation, which is reversible, and where no significant secondary structure change was observed. These results suggested that the interaction between C-terminal and N-terminal regions may play a crucial role in maintaining the overall structure of β-propeller proteins.     

Influenza virus pathogenicity regulated by host cellular proteases,cytokines and metabolites,and its therapeutic options

Influenza A virus (IAV) causes significant morbidity and mortality. The knowledge gained within the last decade on the pandemic IAV(H1N1)2009 improved our understanding not only of the viral pathogenicity but also the host cellular factors involved in the pathogenicity of multiorgan failure (MOF), such as cellular trypsin-type hemagglutinin (HA₀) processing proteases for viral multiplication, cytokine storm, metabolic disorders and energy crisis. The HA processing proteases in the airway and organs for all IAV known to date have been identified. Recently, a new concept on the pathogenicity of MOF, the “influenza virus–cytokine–trypsin” cycle, has been proposed involving up-regulation of trypsin through pro-inflammatory cytokines, and potentiation of viral multiplication in various organs. Furthermore, the relationship between causative factors has been summarized as the “influenza virus–cytokine–trypsin” cycle interconnected with the “metabolic disorders–cytokine” cycle. These cycles provide new treatment concepts for ATP crisis and MOF. This review discusses IAV pathogenicity on cellular proteases, cytokines, metabolites and therapeutic options.     

Enzymatic determination of vitamin A in pharmaceutical formulations with spectrophotometric detection

An enzymatic method for the determination vitamin A (retinol) is reported using soluble and immobilized alcohol dehydrogenase, isolated from rabbit liver. The reaction is based on the oxidation of retinol and simultaneous reduction of NAD⁺ to NADH followed by spectrophotometric detection at 340 nm. The calibration graph was linear over the range of 2.0–10 μM with correlation coefficients of 0.9967 and 0.9992 (n = 5) for soluble and immobilized alcohol dehydrogenase respectively, with relative standard deviations (n = 3) in the range of 0.5–1.2%. The limit of detection was lower than 1.0 μM. The proposed method was applied to determine vitamin A in pharmaceuticals, and the results obtained were in reasonable agreement with the amount labeled. The results were compared using spectrophotometric reference method, and no significant difference was found between the results of the both methods.     

Electrocatalytic reduction of NAD+ at glassy carbon electrode modified with single-walled carbon nanotubes and Ru(III) complexes

A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes and Ruthenium (III) complexes. First, 25 μl of dimethyl sulfoxide–carbon nanotubes solutions (0.4 mg/ml) was cast on the surface of the glassy carbon electrode and dried in air to form a carbon nanotube film at the electrode surface. Then, the glassy carbon/carbon nanotube-modified electrode was immersed into a Ruthenium (III) complex solution (direct deposition) for a short period of time (10–20 s for multiwalled carbon nanotubes and 20–40 s for single-walled carbon nanotubes). The cyclic voltammograms of the modified electrode in aqueous solution shows a pair of well-defined, stable, and nearly reversible redox couple, Ru(III)/Ru(II), with surface-confined characteristics. The attractive mechanical and electrical characteristics of carbon nanostructures and unique properties and reactivity of Ru complexes are combined. The transfer coefficient (α), heterogeneous electron transfer rate constants (k _s), and surface concentrations (Γ) for the glassy carbon/single-walled carbon nanotubes/Ru(III) complex-, glassy carbon/multiwalled carbon nanotubes/Ru(III) complex-, and glassy carbon/Ru(III) complex-modified electrodes were calculated using the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time, and high sensitivity toward the reduction of nicotinamide adenine dinucleotide in phosphate buffer solutions at a pH range of 4–8. The catalytic cathodic current depends on the nicotinamide adenine dinucleotide concentration. In the presence of alcohol dehydrogenase, the modified electrode exhibited a response to addition of acetaldehyde. Therefore, the main product of nicotinamide adenine dinucleotide electroreduction at the Ru(III) complex/carbon nanotube-modified electrode was the enzymatically active NADH. The purposed sensor can be used for acetaldehyde determination.     

镍离子与酵母乙醇脱氢酶的相互作用

不同体系中, 金属离子与蛋白以不同的结合方式相互作用. 酵母乙醇脱氢酶是一个含锌金属酶, 它可催化乙醇脱氢为乙醛的反应. 本文应用紫外-可见光谱、荧光光谱、差示扫描量热法等技术研究了二价镍离子与酵母乙醇脱氢酶的相互作用. 镍离子与酶结合后在320 nm出现了紫外吸收带, 同时荧光光谱反映了酶的构象变化, 紫外与荧光光谱均展现了结合过程的双相动力学. 镍离子与酶的相互作用导致了酶由四聚体向二聚体的解离; 在酶热变性过程中, 镍离子增加了乙醇脱氢酶的变性温度和变性焓. 研究工作揭示了镍离子与酶相互作用复杂和深层的作用机制.     

Determination of the liver cytosolic proteins that bind to p-hydroxyacetophenone

The purpose of the present study was to determine the proteins that bind to acetophenones in the liver. Immobilized p-hydroxyacetophenone (p-HAP) was used as a ligand of affinity chromatography. Analysis using sodium dodesyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that five polypeptides in the liver cytosolic fraction specifically bound to the p-HAP matrix. These polypeptides were digested with Lys-specific protease and used to generate peptide maps by reversed-phase high-performance liquid chromatography. Consequently, identification from a data base of protein sequences revealed that the five polypeptides were glycogen phosphorylase, cytosolic aldehyde dehydrogenase, adenosine kinase, class I alcohol dehydrogenase and glutathione S-transferase A2. In addition to p-HAP, acetylsalicylic acid also displayed a prominent ability to elute these five enzymes from the p-HAP affinity column loaded with the cytosolic fraction of the liver. Thus, p-HAP has affinities to the above liver enzymes and is a useful ligand for analysis of them.     

Activity and Conformation of Yeast Alcohol Dehydrogenase (YADH) Entrapped in Reverse Micelles

Yeast alcohol dehydrogenase (YADH) solubilized in reverse micelles of aerosol OT (i.e., AOT or sodium bis (2-ethyl hexyl) sulfosuccinate) in isooctane has been shown to be catalytically more active than that in aqueous buffer under optimum conditions of pH, temperature, and water content in reverse micelles. Studies of the secondary structure conformational changes of the enzyme in reverse micelles have been made from circular dichroism spectroscopy. It has been seen that the conformation of YADH in reverse micelles is extremely sensitive to pH, temperature, and water content. A comparison has been made between the catalytic activity of the enzyme and the α-helix content in the conformation and it has been observed that the enzyme is most active at the maximum α-helix content. While the β-sheet content in the conformation of the entrapped enzyme was found to be dependent on the enzyme–micelle interface interaction, the α-helix and random coil conformations are governed by the degree of entrapment and the extent of rigidity provided by the micelle core to the enzyme structure.