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At least 217 records · Page 12Linked to original sources
PubMed1999

Remarkable thermostability of bioelectrodes based on enzymes immobilized within hydrophobic semi-solid matrices.

An enhanced resistance to thermal denaturation was investigated for enzymes immobilized within hydrophobic semi-solid matrices compared with both free enzymes and polymer-entrapped enzymes. The bioelectrodes based on the immobilization of glucose oxidase, lactate oxidase, alcohol oxidase, polyphenol oxidase, peroxidase and L-amino acid oxidase within a carbon-paste matrix were constructed to examine their thermal stabilitiy at 60 degrees C or 80 degrees C. The rhodium/glucose oxidase-containing carbon-paste electrode was found to offer a remarkable stability when incubated at 60 degrees C over a long period of 4 months, with only a decrease of approx. 15% in activity. The comparative studies suggest that thermal stabilization established by this enzyme-immobilization procedure varies with the enzyme's inherent stability, the incubation temperature and the immobilizing reagent, such as pasting liquid.

Alcohol Oxidoreductases↗
PubMed1991

Immobilized enzyme system for determination of sialic acid in serum or urine.

An immobilized enzyme system has been developed and employed to determine the concentration of sialic acid (N-acetylneuraminic acid) in human serum and urine. Two enzyme pairs, neuramindiase-Neu-5-Ac lyase and pyruvate oxidase-peroxidase, have been respectively co-immobilized onto 1,12-aminododecane-agarose with glutaraldehyde. The relative specific activity of the co-immobilized neuraminidase and Neu-5-Ac lyase were 60% and 78%, and those of pyruvate oxidase and peroxidase were 50% and 95% of the corresponding soluble enzymes, respectively. The optimal reaction pH at 37 degrees C for each of the co-immobilized enzymes was about one pH unit higher than that of the corresponding soluble enzyme. The optimal reaction temperature of each enzyme was increased as a result of immobilization. The thermal stability at 45 degrees C of the immobilized neuraminidase, Neu-5-Ac lyase, pyruvate oxidase, and peroxidase were increased 80-, 83-, 115-, and 147-fold, respectively. Km and Vm of each immobilized and co-immobilized enzyme have also been determined. The system provided a convenient and rapid method to determine the concentration of total sialic acid without pretreatment of the sample. The results correlated satisfactorily with those obtained by using a soluble enzyme system. The co-immobilized enzymes were stable for at least 1 year of 500 tests when used repeatedly. The system is thus a reproducible and reliable novel assay method for sialic acid in the serum or urine sample.

Enzymes, Immobilized↗
PubMed1998

Purification and characterization of a nylon-degrading enzyme.

A nylon-degrading enzyme found in the extracellular medium of a ligninolytic culture of the white rot fungus strain IZU-154 was purified by ion-exchange chromatography, gel filtration chromatography, and hydrophobic chromatography. The characteristics of the purified protein (i.e., molecular weight, absorption spectrum, and requirements for 2,6-dimethoxyphenol oxidation) were identical to those of manganese peroxidase, which was previously characterized as a key enzyme in the ligninolytic systems of many white rot fungi, and this result led us to conclude that nylon degradation is catalyzed by manganese peroxidase. However, the reaction mechanism for nylon degradation differed significantly from the reaction mechanism reported for manganese peroxidase. The nylon-degrading activity did not depend on exogenous H2O2 but nevertheless was inhibited by catalase, and superoxide dismutase inhibited the nylon-degrading activity strongly. These features are identical to those of the peroxidase-oxidase reaction catalyzed by horseradish peroxidase. In addition, alpha-hydroxy acids which are known to accelerate the manganese peroxidase reaction inhibited the nylon-degrading activity strongly. Degradation of nylon-6 fiber was also investigated. Drastic and regular erosion in the nylon surface was observed, suggesting that nylon is degraded to soluble oligomers and that nylon is degraded selectively.

Amidohydrolases↗
PubMed1980

Oxygen activation by sulfhydryl oxidase and the enzyme's interaction with peroxidase.

Sulfhydryl oxidase is a metalloglycoprotein in milk which catalyzes oxidation of thiols to their corresponding disulfides using molecular oxygen as an electron acceptor. Cysteine, peptides, and proteins all serve as substrates for this oxidative activity. Investigation of the various possible active oxygen species suggests that the enzyme-bound forms of singlet oxygen and a hydroperoxy group may be produced during catalysis. However, the possible intermediate superoxide anions or hydroxyl radicals did not appear to be formed. Evidence was obtained for a direct interaction between sulfhydryl oxidase and horseradish peroxidase which results in an enhancement of the thiol oxidative activity. This interaction also induced a change in the peroxidase absorption spectra consistent with formation of the horseradish peroxidase-II form of the enzyme. Stimulation of oxidase activity also was observed in the presence of oxytocin and certain concentrations of oxidized glutathione.

Animals↗
PubMed2002

Subcellular localization and isoenzyme pattern of peroxidase and polyphenol oxidase in beet root (Beta vulgaris L.).

The two enzymes involved in enzymatic browning reactions, polyphenol oxidase (PPO) and peroxidase (PO), have been partially purified and extracted from different fractions of beet root. PPO is mainly located in the membrane fraction, and it was also found in the soluble fraction. In both cases PPO was in its latent state. However, PO activity was higher in the soluble fraction than in the membrane fraction. Nevertheless, the highest values of specific activity for PO were obtained from the solubilized enzyme from acetone powders. Under native isoelectric focusing (IEF), several PPO isoenzymes were present in the pH range of 4.8-5.8. All of these isoenzymes shared a single band with a similar apparent mass under sodium dodecyl sulfate-polyacrylamide gel electrophoresis. PO was also analyzed by IEF, showing a complex isoenzyme pattern in all fractions. The characteristic basic PO isoenzyme of high pI found in both the soluble fraction and the solubilized enzyme from acetone powders was not detected in the membrane fraction. The kinetic characterization of PPO and PO from all fractions was carried out.

Beta vulgaris↗
PubMed1980

Deviations from Michaelis-Menten kinetics. The possibility of complicated curves for simple kinetic schemes and the computer fitting of experimental data for acetylcholinesterase, acid phosphatase, adenosine deaminase, arylsulphatase, benzylamine oxidase, chymotrypsin, fumarase, galactose dehydrogenase, beta-galactosidase, lactate dehydrogenase, peroxidase and xanthine oxidase.

The possible graph shapes for one-site/two-state and substrate-modifier models are discussed. The two-state model is a version of the Monod-Wyman-Changeux model and gives a rate equation with 240 denominator terms. Discussion in terms of K and V effects is not possible. A simplified version of the mechanism can be shown to give v-versus-[S] curves that are either sigmoid or non-sigmoid. They may show substrate inhibition or no final maximum, and the double-reciprocal plots can be concave up or down. The corresponding binding model is determined by only two constants and gives a linear double-reciprocal plot. The substrate-modifier mechanism is a simple example of a mechanism where inclusion of catalytic steps leads to a genuine increase in degree of the rate equation. The v-versus-[S] curve can show such complexities as two maxima and a minimum, and the double-reciprocal plot can cross its asymptote twice, proving the rate equation to be 4:4. A simplified version is 3:3, and analysis shows that at least 18 of the 27 double-reciprocal plots that can arise with 3:3 functions are possible with this particular mechanism. Representative double-reciprocal and Scatchard plots are presented for several sets of rate-constant values. It is concluded that relatively simple mechanisms give pseudo-steady-state rate equations of high degree and considerable complexity. With extended ranges of substrate concentrations there is every reason to believe that experimental data would show the sort of deviations from Michaelis-Menten kinetics seen with calculated curves for such simple mechanisms. Narrow ranges of substrate concentration, on the other hand, would lead to inflexions and curvature being overlooked. It is not possible to discuss such deviations from Michaelis-Menten kinetics in terms of kinetic constants such as Km and V, and, in general, it is also difficult to see any simple way to explain intuitively such features as sigmoidicity, substrate inhibition, double-reciprocal convexity and decrease in degree by cancellation of common factors between numerator and denominator of rate equations. These conclusions apply with even more force when catalytic steps are included, for then the rate equations, are for multi-site mechanisms, of higher degree, allowing increasingly complex curve shapes. A number of enzymes were studied and initial-rate data were fitted by computer.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholinesterase↗
PubMed2004

Catalase-peroxidases (KatG) exhibit NADH oxidase activity.

Catalase-peroxidases (KatG) produced by Burkholderia pseudomallei, Escherichia coli, and Mycobacterium tuberculosis catalyze the oxidation of NADH to form NAD+ and either H2O2 or superoxide radical depending on pH. The NADH oxidase reaction requires molecular oxygen, does not require hydrogen peroxide, is not inhibited by superoxide dismutase or catalase, and has a pH optimum of 8.75, clearly differentiating it from the peroxidase and catalase reactions with pH optima of 5.5 and 6.5, respectively, and from the NADH peroxidase-oxidase reaction of horseradish peroxidase. B. pseudomallei KatG has a relatively high affinity for NADH (Km=12 microm), but the oxidase reaction is slow (kcat=0.54 min(-1)) compared with the peroxidase and catalase reactions. The catalase-peroxidases also catalyze the hydrazinolysis of isonicotinic acid hydrazide (INH) in an oxygen- and H2O2-independent reaction, and KatG-dependent radical generation from a mixture of NADH and INH is two to three times faster than the combined rates of separate reactions with NADH and INH alone. The major products from the coupled reaction, identified by high pressure liquid chromatography fractionation and mass spectrometry, are NAD+ and isonicotinoyl-NAD, the activated form of isoniazid that inhibits mycolic acid synthesis in M. tuberculosis. Isonicotinoyl-NAD synthesis from a mixture of NAD+ and INH is KatG-dependent and is activated by manganese ion. M. tuberculosis KatG catalyzes isonicotinoyl-NAD formation from NAD+ and INH more efficiently than B. pseudomallei KatG.

Bacterial Proteins↗
PubMed1998

Magnetic field perturbations as a tool for controlling enzyme-regulated and oscillatory biochemical reactions.

The feasibility of magnetic field perturbations as a tool for controlling enzyme-regulated and oscillatory biochemical reactions is studied. Our approach is based on recent experimental results that revealed magnetic field effects on the in vitro activity of enzyme systems in accordance with the radical pair mechanism. A minimum model consisting of two coupled enzyme-regulated reactions is discussed that combines, in a self-consistent manner, magnetic field-sensitive enzyme kinetics with non-linear dynamical principles. Furthermore, a simple detector mechanism is described that is capable of responding to an oscillatory input. Results reveal that moderate-strength magnetic fields (B=1-100 mT) may effectively alter the dynamics of the system. In particular, a response behavior is observed that depends on: (1) the combination of static and time-varying magnetic fields; (2) the field amplitude; and (3) the field frequency in a non-linear fashion. The specific response behavior is critically determined by the biochemical boundary conditions as defined by the kinetic properties of the system. We propose an experimental implementation of the results based on the oscillatory peroxidase-oxidase reaction controlled by the enzyme horseradish peroxidase.

Journal Article↗
PubMed2006

[Comparative study on GOD-trinder method for measuring glucose in serum with different benzene-original phenols].

Comparative studies were carried out on GOD-trinder method for measuring glucose in serum with four different kinds of benzene-original phenols-phenyl hydroxide, 2,4-dichlorophenol, 2,6-dichlorophenol and resorcinol. It is shown that when the three coloring systems-phenyl hydroxide, 2,4-dichlorophenol or resorcinol coupling with glucose oxidase-peroxidase-4-a minoantipyrine-hydrogen peroxide (GOD-POD-4-AA-H2O2) respectively were used for clinical assay of glucose in serum, the determination results showed no significant differences (P > 0.05). Compared with phenyl hydroxide, the coloring system of 2,4-dichlorophenol is better in the aspects of sensitivity, precision and accuracy; the resorcinol system has lower sensitivity with the advantage of faster detecting velocity, and larger linear range, and can be used for on-line rapid analysis of samples with more concentrated glucose in industry.

Blood Glucose↗
PubMed1990

High density lipoprotein is a scavenger of superoxide anions.

Present work describes a new property of HDL to act as a scavenger of O2- free radicals in vitro. This lipoprotein prevents both enzymic and non-enzymic generation of O2- anions as evidenced by inhibition of xanthine oxidase, peroxidase, peroxidation of pyrogallol and phenazine methosulphate-NADH reaction. Ascorbate stimulated MDA formation in microsomes has been shown to be suppressed by HDL and these effects are comparable with that of BHA.

Animals↗
PubMed1992

Active-site structural comparison of streptococcal NADH peroxidase and NADH oxidase. Reconstitution with artificial flavins.

The apoproteins of the streptococcal NADH peroxidase (H2O2----2H2O) and NADH oxidase (O2----2H2O) stabilize the neutral forms of 6-hydroxy- and 6-mercapto-FAD, respectively. The redox behavior of the 6-hydroxy-FAD peroxidase closely mimics that of the native enzyme with both dithionite and NADH. Both oxidase and peroxidase preferentially stabilize the N(1)-protonated p-quinonoid species of 8-mercapto-FAD, and the 8-position of the bound flavin is accessible to solvent in both proteins. The 8-mercapto-FAD peroxidase yields an EH2 spectrum on reduction virtually identical to that seen with 8-mercapto-FAD glutathione reductase, but no distinct EH2.NADH form appears. The dramatic decreases in reactivity at the flavin 2- and 4-positions for both the peroxidase and the oxidase, assessed with the reconstituted 2- and 4-thio-FAD enzymes, suggest that these positions are buried by elements of both protein structures. Furthermore, reconstitution of the peroxidase with the higher potential 2- and 4-thioflavins yields enzyme forms which are fully reducible with 1.4 eq of NADH/FAD, giving rise to stable thio-FADH2.NAD+ complexes. This behavior closely mimics that of the native NADH oxidase and provides further evidence supporting the hypothesis that a major functional distinction between the two structurally related proteins is determined by the redox potential and/or NADH reactivity of the bound flavin coenzyme.

Binding Sites↗
PubMed1996

Oxygenation activities of chicken polymorphonuclear leukocytes investigated by selective chemiluminigenic probes.

The redox metabolism of myeloperoxidase-deficient rooster (chicken) polymorphonuclear leukocytes (PMNL) was analyzed by differential chemiluminigenic probes. Chicken complement-opsonified zymosan, a phagocytosable particulate stimulus, and phorbol myristate acetate, a chemical stimulus, were used to activate the PMNL respiratory burst. The two probes used were luminol (5-amino-2,3-dihydro-1,4-phthalazinedione), a general probe of oxidase-peroxidase activities, and lucigenin (dimethylbiacridinium binitrate), a selective probe of oxidase activity. Rooster PMNLs yielded dimethylbiacridinum binitrate-dependent chemiluminescence (CL) comparable to those of myeloperoxidase-containing human PMNLs after stimulation with opsonified zymosan and to a lesser extent with phorbol myristate acetate. However, the luminol-dependent CL of opsonified zymosan or phorbol myristate acetate-stimulated rooster PMNLs were approximately two orders of magnitude lower than responses observed with human PMNLs. At physiologic pH, luminol is a highly sensitive, but not specific, probe of myeloperoxidase activity. Rooster erythrocytes yielded no CL with any of the probe-stimulus combinations described. Rooster PMNL viability and oxygen were required for CL. No strong correlation could be drawn between CL responses and eosinophil leukocyte concentration. The major conclusion is that rooster PMNLs, which do not have myeloperoxidase, present a significant and reproducible oxidative burst to chemical and particulate stimuli. Although lacking in peroxidase, rooster PMNLs can still present small luminol-dependent responses.

Acridines↗
PubMed1980

Studies on cartilage formation. XXII. Investigations of certain oxidative metabolic processes in regenerating articular cartilage.

The distal articular surface of the femur was surgically removed in 57 dogs. Succinate dehydrogenase and cytochrome oxidase activities were assayed on postoperative days 7, 20, 26, 33 and 70 in the regenerating, chondrifying articular surface and in the granulation tissue adhering to the capsule. In the 70-day samples, the cyanide-induced inhibition of oxygen consumption was determined and enzyme histochemical reactions (cytochrome oxidase, monoamine oxidase, xanthine oxidase, peroxidase and "catalase") were performed. The succinate dehydrogenase activity was the highest in the early postoperative stage in both tissues. This was followed by a definite decrease and a subsequent significant increase in activity when chondrification took place. Measurement of cytochrome oxidase activity could not reveal any convincing result, presumably because of the properties of the tissues studied. The oxygen consumption by the chondrifying articular surface at 70 days was inhibited to about 50% by cyanide, and about 90% inhibition was observed in the tissue adhering to the capsule. The cells of the regenerating articular surface possess cytochrome oxidase and a cyanide- (and sodium azide-) resistant oxidase activity. The enzyme activity of the cartilaginous islets exceeded that of their connective tissue environment. The cytochrome oxidase activity increased in the cells during cartilage differentiation. Presumably, some further cyanide-sensitive and cyanide-resistant oxidases are present in chondroblasts and young chondrocytes.

Animals↗
PubMed1982

Peroxidase and IAA oxidase in germinating seeds of Cicer arietinum L.

Peroxidase and indole acetic oxidase (IA oxidase) activities in seeds of Cicer arietinum L. were studied at 72 h of germination. Both activities behaved differently in relation to optimum pH, stability against temperature and time of storage of 4 degrees C. Disc electrophoresis on polyacrilamide gel showed the existence of five anionic and three cationic isoenzymes with peroxidase activity by using benzidine as substrate; three of the anionic isoenzymes and one cationic isoenzyme possessed a simultaneous IAA oxidase activity as well.

Chromatography, Gel↗