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At least 1,693 records · Page 94Linked to original sources
PubMed1982

Ozone-induced formation of O,O'-dityrosine cross-linked in proteins.

Treatment of spectrin, insulin, glucagon and ribonuclease with ozone results in covalent cross-linking of these proteins. This cross-linking is not reversed by treatment with dithiothreitol and thus can not be ascribed to -S-S- bond formation. A concomitant O,O'-dityrosine formation is observed by spectrofluorometric analysis of the protein and by amino acid analysis and thin-layer chromatography of hydrolyzed protein samples. It is highly probable that the observed protein cross-linking should be attributed to interpeptide O,O'-dityrosine bonds. Several authors have shown before that oxidation of proteins with horseradish peroxidase and H2O2 also leads to O,O'-dityrosine formation. Peroxidase-induced O,O'-dityrosine formation in galactose oxidase (d-galactose:oxygen 6-oxidoreductase, EC 1.1.3.9) causes a strong increase of enzyme activity. In accordance with these observations ozone treatment of galactose oxidase also leads to O,O'-dityrosine formation with a concomitant 8-fold increase of enzyme activity.

Amino Acids↗
PubMed1986

The superoxide dismutase activity of myeloperoxidase; formation of compound III.

The reaction of superoxide anions with myeloperoxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7), which results in the formation of Compound III of myeloperoxidase, was investigated. It is shown that myeloperoxidase has a high affinity for superoxide anions because formation of Compound III was only partially inhibited by high concentrations of superoxide dismutase. Furthermore, when superoxide anions were generated in a mixture of both cytochrome c and myeloperoxidase in the absence of Cl-, only Compound III was formed and reduction of cytochrome c was not observed. In the presence of Cl-, Compound III was also formed and reduction of cytochrome c was inhibited. From the results described in this paper we conclude that Compound III is able to react with superoxide anions, probably resulting in formation of an intermediate (Compound I) which is catalytically active in the oxidation of Cl- to yield hypochlorous acid (HOCl). Because Compound III of myeloperoxidase is formed in phagocytosing neutrophils (Winterbourn, C.C., Garcia, R.C. and Segal, A.W. (1985) Biochem. J. 228, 583-592) we propose that, in vivo, myeloperoxidase also acts as a superoxide dismutase, and via formation of Compound I uses superoxide anions in the formation of HOCl.

Catalase↗
PubMed1989

Difference in hydrogen peroxide release between human neutrophils and neutrophil cytoplasts following calcium ionophore activation. A role of the subcellular granule in activation of the NADPH-oxidase in human neutrophils?

The role of subcellular granule in the capacity to generate reactive oxygen metabolites in human granulocytes was studied using normal cells and organell-free neutrophil cytoplasts. The cytoplasts are devoid of granules but have an intact ligand-receptor coupling mechanism. Both the chemotactic peptide formylmethionylleucylphenylalanine (FMLP) and the ionophore ionomycin induced a chemiluminescence response in normal cells, but only FMLP stimulation was associated with any notable hydrogen peroxide production. However, in the presence of azide, a potent inhibitor of the hydrogen peroxide-consuming enzymes, catalase and myeloperoxidase, a pronounced release of hydrogen peroxide was also induced by ionomycin. The response of cytoplasts to FMLP proceeded with a rate and time-course similar to those seen in intact cells, whereas in response to ionomycin they produced very low quantities of hydrogen peroxide, even in the presence of azide. Analysis of the data presented in this study leads to the following conclusion: (i) FMLP, which acts through cell surface receptors, causes the cells to produce oxygen metabolites, which, to a large extent, are released from the cells, a process that is not dependent on subcellular granule; and (ii) ionomycin, which bypasses cell surface receptors, is also capable of stimulating hydrogen peroxide formation that is granule-dependent and that is retained inside the cells.

Azides↗
PubMed1986

Transient response of bienzyme electrodes.

A mathematical model of the transient response of amperometric bienzyme electrodes with a consecutive, cyclic and parallel substrate conversion is developed. At high catalytic activity the kinetic behavior of consecutive and parallel conversion is close to the substance diffusion through the inert membrane, and the kinetics of cyclic conversion are 3.54 times slower. At low substrate conversion rates the electrodes' response is markedly retarded. Mathematical modeling results are compared with the experimental data on the kinetic behavior of amperometric enzyme electrodes in the membranes of which the consecutive and cyclic conversions of glucose and nicotinamide adenine dinucleotide, respectively, take place.

Alcohol Dehydrogenase↗
PubMed1990

A clinical comparison of the performance of four blood glucose reagent strips.

The widespread use of visually read blood glucose reagent strips for initiation of emergent treatment of hypoglycemia and hyperglycemia has produced concern over the accuracy of this method. This study evaluated the accuracy of Chemstrip bG (Bio-Dynamics, Boehringer Mannheim, Indianapolis, IN), Dextrostix (Ames, Miles Laboratories, Elkhart, IN), Glucostix (Ames), and Visidex II (Ames) as compared with hospital laboratory values in an emergency department (ED) setting. Blood samples from 96 ED patients were tested for glucose concentration by each of the four strips and by the hospital laboratory. Each strip was evaluated for sensitivity, specificity, correlation coefficient (r), 95% confidence intervals, and kappa statistic (kappa, a measure of agreement between nonparametric data) using laboratory values as reference. In addition, six observers scored each strip for ease of interpretation using an ordinal scale of 1 (poor) to 4 (excellent). From the samples, no patients were hypoglycemic (less than or equal to 60 mg/dL), 83 were euglycemic (greater than 60 and less than 160 mg/dL), and 13 were hyperglycemic (greater than or equal to 160 mg/dL). Results suggest that over the range of glucose concentration sampled, there is good to excellent correlation with laboratory values for all strips except Dextrostix. The lower r value for Dextrostix is in part artifact due to limitation of its range of measurement to less than or equal to 250 mg/dL. Decreased accuracy for all strips in the hyperglycemic range may have been attributable to small sample size. Chemstrip bG and Visidex II were found to be subjectively easier to interpret.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Glucose↗
PubMed2003

Chemical basis of inflammation-induced carcinogenesis.

Chronic inflammation induced by biological, chemical, and physical factors has been associated with increased risk of human cancer at various sites. Inflammation activates a variety of inflammatory cells, which induce and activate several oxidant-generating enzymes such as NADPH oxidase, inducible nitric oxide synthase, myeloperoxidase, and eosinophil peroxidase. These enzymes produce high concentrations of diverse free radicals and oxidants including superoxide anion, nitric oxide, nitroxyl, nitrogen dioxide, hydrogen peroxide, hypochlorous acid, and hypobromous acid, which react with each other to generate other more potent reactive oxygen and nitrogen species such as peroxynitrite. These species can damage DNA, RNA, lipids, and proteins by nitration, oxidation, chlorination, and bromination reactions, leading to increased mutations and altered functions of enzymes and proteins (e.g., activation of oncogene products and/or inhibition of tumor-suppressor proteins) and thus contributing to the multistage carcinogenesis process. Appropriate treatment of inflammation should be explored further for chemoprevention of human cancers.

DNA Damage↗
PubMed1991

Cytochromes c of Nitrobacter winogradskyi and Thiobacillus novellus: structure, function and evolution.

The amino acid sequences of Thiobacillus novellus and Nitrobacter winogradskyi cytochromes c have been compared with those of cytochromes c from several other organisms. The two bacterial cytochromes resemble eukaryotic cytochromes c; 49 amino-acid residues are identical between T. novellus and horse cytochromes c, and 50 residues identical between N. winogradskyi and horse cytochromes c. However, their reactivity with cow cytochrome c oxidase is about 80% lower than the reactivity of eukaryotic cytochromes c with the cow mitochondrial oxidase, while they react with yeast cytochrome c peroxidase as rapidly as eukaryotic cytochromes c. The numbers of identical amino-acid residues between T. novellus and animal cytochromes c are 45-53 and those between N. winogradskyi and animal cytochromes c 47-53, while those between the two bacterial cytochromes and yeast and protozoan cytochromes c are around 40. Thus, N. winogradskyi and T. novellus cytochromes c are more similar to animal cytochromes c than to yeast and protozoan cytochromes c on the basis of the amino-acid sequence.

Amino Acid Sequence↗
PubMed2006

Logic gates and elementary computing by enzymes.

Different selected enzymes, glucose oxidase (GOx), catalase (Cat), glucose dehydrogenase (GDH), horseradish peroxidase (HRP), and formaldehyde dehydrogenase (FDH), are used alone or coupled to construct eight different logic gates. The added substrates for the respective enzymes, glucose and H(2)O(2), act as the gate inputs, while the biocatalytically generated gluconic acid or NADH are the output signals that follow the operation of the gates. Different enzyme-based gates are XOR, INHIBIT A, INHIBIT B, AND, OR, NOR, Identity and Inverter gates. By combining the AND and XOR or the XOR and INHIBIT A gates, the half-adder and half-subtractor are constructed, respectively, opening the way to elementary computing by the use of enzymes.

Animals↗
PubMed2004

Microfluidic biosensing systems. Part I. Development and optimisation of enzymatic chemiluminescent micro-biosensors based on silicon microchips.

Chemiluminescent (CL) enzyme-based flow-through microchip biosensors (micro-biosensors) for detection of glucose and ethanol were developed for the purpose of monitoring real-time production and release of glucose and ethanol from microchip immobilised yeast cells. Part I of this study focuses on the development and optimisation of the micro-biosensors in a microfluidic sequential injection analysis (microSIA) system. Glucose oxidase (GOX) or alcohol oxidase (AOX) was co-immobilised with horseradish peroxidase (HRP) on porous silicon flow through microchips. The hydrogen peroxide produced from oxidation of the corresponding analyte (glucose or ethanol) took part in the chemiluminescent (CL) oxidation of luminol catalysed by HRP enhanced by addition of p-iodophenol (PIP). All steps in the microSIA system, including control of syringe pump, multiposition valve (MPV) and data readout, were computer controlled. The influence of flow rate and luminol- and PIP concentration were investigated using a 2(3)-factor experiment using the GOX-HRP sensor. It was found that all estimated single factors and the highest order of interaction were significant. The optimum was found at 250 microM luminol and 150 microM PIP at a flow rate of 18 microl min(-1), the latter as a compromise between signal intensity and analysis time. Using the optimised system settings one sample was processed within 5 min. Two different immobilisation chemistries were investigated for both micro-biosensors based on 3-aminopropyltriethoxsilane (APTS)- or polyethylenimine (PEI) functionalisation followed by glutaraldehyde (GA) activation. GOX-HRP micro-biosensors responded linear in a log-log format within the range 10-1000 microM glucose. Both had an operational stability of at least 8 days, but the PEI-GOX-HRP sensor was more sensitive. The AOX-HRP micro-biosensors responded linear (log-log) in the range between 1 and 10 mM ethanol, but the PEI-AOX-HRP sensor was in general more sensitive. Both sensors had an operational stability of at least 8 h, but with a half-life of 2-3 days.

Biosensing Techniques↗