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Michaelis-Menten Constant (michaelis-menten + constant)

Distribution by Scientific Domains
Chemistry60%
Life Sciences40%

Selected Abstracts

Glucose Biosensor Mediated by 1,2-Diferrocenylethane in a Sono-Gel Composite Electrode

ELECTROANALYSIS, Issue 2-3 2007
Barbara Ballarin
Abstract An amperometric glucose biosensor was constructed based on a renewable carbon composite sono-gel matrix incorporating 1,2-diferrocenylethane as electron transfer mediator between the electrode and the active site of glucose oxidase. The enzyme was immobilized on the electrode surface by cross-linking with glutaraldehyde and bovine serum albumin. The process parameters for the fabrication of the biosensor and the influence of various experimental conditions (i.e., pH, temperature, operating potential) were investigated. Cyclic voltammetry and amperometric measurements were used to study the response of the glucose sensor, which displayed fast response time and good reproducibility. The analytical performances and the apparent Michaelis-Menten constant of the biosensor were evaluated. [source]

Purification and characterization of tannin acyl hydrolase from Aspergillus niger MTCC 2425

JOURNAL OF BASIC MICROBIOLOGY, Issue 6 2003
Rita Bhardwaj
The present investigation was carried out for increasing the yield of tannase of Aspergillus niger and the physico-chemical characterization of this enzyme. Homogenization and detergent pretreatments did not have any remarkable effect on the extraction of enzyme protein. However, extraction of fungal pigments and proteins was observed to have high pH dependence, and maximum enzyme extraction was obtained at pH 5.5. The two-step purification protocol gave 51-fold purified enzyme with a yield of 20%. The total tannase activity was made up of nearly equal activity of esterase and depsidase. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of purified tannase protein indicated it to be made up of two polypeptides of molecular weight 102 and 83 kDa. Based on the Michaelis-Menten constant (Km) of tannase for three substrates tested, tannic acid was the best substrate with Km of 2.8 × 10,4M, followed by methyl gallate and propyl gallate. The inhibition was maximum for CaCl2 (58%) whereas EDTA had no modulatory effect on tannase activity. The inhibitor binding constant (KI) of CaCl2 was 5.9 × 10,4M and the inhibition was of noncompetitive type. [source]

Immobilization and Characterization of Glucose Oxidase on Single-Walled Carbon Nanotubes and Its Application to Sensing Glucose

CHINESE JOURNAL OF CHEMISTRY, Issue 4 2007
Shu-Na Liu
Abstract The negatively charged (at pH 8.2) glucose oxidase (GOx, pI ca. 4.2) was assembled onto the surface of single-walled carbon nanotubes (SWNT), which was covered (or wrapped) by a layer of positively charged polyelectrolyte poly(dimethyldiallylammonium chloride) (PDDA), via the electrostatic interaction forming GOx-PDDA- SWNT nanocomposites. Fourier transform infrared (FTIR), UV-Vis and electrochemical impedance spectroscopy (EIS) were used to characterize the growth processes of the nanocomposites. The results indicated that GOx retained its native secondary conformational structure after it was immobilized on the surface of PDDA-SWNT. A biosensor (Nafion-GOx-PDDA-SWNT/GC) was developed by immobilization of GOx-PDDA-SWNT nanocomposites on the surface of glassy carbon (GC) electrode using Nafion (5%) as a binder. The biosensor showed the electrocatalytic activity toward the oxidation of glucose under the presence of ferrocene monocarboxylic acid (FcM) as an electroactive mediator with a good stability, reproducibility and higher biological affinity. Under an optimal condition, the biosensor could be used to detection of glucose, presenting a typical characteristic of Michaelis-Menten kinetics with the apparent Michaelis-Menten constant of KappMca. 4.5 mmol/L, with a linear range of the concentration of glucose from 0.5 to 5.5 mmol/L (with correlation coefficient of 0.999) and the detection limit of ca. 83 µmol/L (at a signal-to-noise ratio of 3). Thus the biosensor was useful in sensing the glucose concentration in serum since the normal glucose concentration in blood serum was around 4.6 mmol/L. The facile procedure of immobilizing GOx used in present work would promote the developments of electrochemical research for enzymes (proteins), biosensors, biofuel cells and other bioelectrochemical devices. [source]

Carbon Ceramic Electrodes Modified with Laccase from Trametes hirsuta: Fabrication, Characterization and Their Use for Phenolic Compounds Detection

ELECTROANALYSIS, Issue 9 2007
Behzad Haghighi
Abstract Fungal laccase (Lc) from the basidiomycete Trametes hirsuta was immobilized on top of a carbon ceramic electrode using physical absorption. Direct, unmediated heterogeneous electron transfer between Lc and the carbon ceramic electrode (CCE) under aerobic conditions was shown. The bioelectrocatalytic reduction of oxygen on Lc-CCE started at about 430,mV vs. Ag|AgCl|KClsat at pH,3.5 and moved with about 57,mV in the cathodic region per pH unit. The Lc-modified CCE was then used as a biosensing detection element in a single line flow injection system for the amperometric determination of a variety of phenolic substrates of the enzyme. The experimental conditions were studied and optimized for catechol serving as a model compound. Statistical aspects were applied and the sensor characteristics and Michaelis-Menten constants of the investigated phenolic compounds were calculated and compared with those obtained for solid graphite electrodes modified with Trametes hirsuta laccase. The results showed that the CCE based biosensor in comparison with the solid graphite based biosensor offers a lower detection limit, a wider linear dynamic range, and excellent operational stability with no sensor passivation, indicating that the sol,gel lattice improves the electrochemical behavior of the biosensor. [source]

Biosynthesis reaction mechanism and kinetics of deoxynucleoside triphosphates, dATP and dGTP

BIOTECHNOLOGY & BIOENGINEERING, Issue 4 2005
Jie Bao
Abstract The enzyme reaction mechanism and kinetics for biosyntheses of deoxyadenosine triphosphate (dATP) and deoxyguanosine triphosphate (dGTP) from the corresponding deoxyadenosine diphosphate (dADP) and deoxyguanosine diphosphate (dGDP) catalyzed by pyruvate kinase were studied. A kinetic model for this synthetic reaction was developed based on a Bi-Bi random rapid equilibrium mechanism. Kinetic constants involved in this pyruvate kinase catalyzed phosphorylation reactions of deoxynucleoside diphosphates including the maximum reaction velocity, Michaelis-Menten constants, and inhibition constants for dATP and dGTP biosyntheses were experimentally determined. These kinetic constants for dATP and dGTP biosyntheses are of the same order of magnitude but significantly different between the two reactions. Kinetic constants involved in ATP and GTP biosyntheses as reported in literature are about one order of magnitude different from those involved in dATP and dGTP biosyntheses. This enzyme reaction requires Mg2+ ion and the optimal Mg2+ concentration was also determined. The experimental results showed a very good agreement with the simulation results obtained from the kinetic model developed. This kinetic model can be applied to the practical application of a pyruvate kinase reaction system for production of dATP and dGTP. There is a significant advantage of using enzymatic biosyntheses of dATP and dGTP as compared to the chemical method that has been in commercial use. © 2005 Wiley Periodicals, Inc. [source]