Peroxidase, enzyme reaction

Nitric oxide and nitrite react with other peroxidase enzymes such as horseradish peroxidase (HRP) (138a,139), lactoperoxidase (138a) and eosinophil peroxidase (140) similarly. The rate constants for reaction of NO with compounds I and II in HRP were found to be 7.0 x 105M 1s 1 and 1.3 x 106M 1s 1, respectively (139). Catalytic consumption of NO as measured by an NO sensitive electrode in the presence of HRP compounds I and II is shown in Fig. 5 where accelerated consumption of NO is achieved even in deoxygenated solutions (140). 

A number of autoxidation reactions exhibit exotic kinetic phenomena under specific experimental conditions. One of the most widely studied systems is the peroxidase-oxidase (PO) oscillator which is the only enzyme reaction showing oscillation in vitro in homogeneous stirred solution. The net reaction is the oxidation of nicotinamide adenine dinucleotide (NADH), a biologically vital coenzyme, by dioxygen in a horseradish peroxidase enzyme (HRP) catalyzed process ... 

The technique described here is for use with monoclonal primary antibodies of mouse origin, but can easily be adapted for use with polyclonal antibodies from other species (i.e., rabbit). This method uses a secondary biotin-labeled antibody and a detection system that employs a biotin-avidin horseradish peroxidase complex linker step, the so-called ABC (avidin-biotin complex) detection system (5) (see Chapter 25). In this detection system, avidin acts as a bridge between the biotinylated secondary antibody and a biotin-labeled peroxidase enzyme. The anchored enzyme, in the presence of H2O2 can then convert the substrate, diaminobenzidine, to a brown or black reaction product that is easily identifiable in the tissue section. 

In an enzymic reaction catalysed by glutathione peroxidase, GSH reacts with peroxides and becomes oxidized to form a dimer (GSSG) linked by a disulfide bridge. 

Inhibition of enzyme activity was not used to assess the antibody-antigen reaction of lignin-peroxidase, as the addition of control serum to enzyme reaction mixtures increased the pH above the pH specificity of the... 

Thionamide drugs interfere with peroxidase-catalyzed reactions. In the thyroid gland, they inhibit the activity of the enzyme TPO, which is required for the intrathyroidal oxidation of I , the incorporation of I into Tg, and the coupling of iodotyrosyl residues to form thyroid hormones. Thus, these drugs inhibit thyroid hormone synthesis and with time, also secretion. Propylthiouracil, but not methimazole, also inhibits Dl, which deiodinates T4 to Tj. Because of this additional action, propylthiouracil is often used to provide a rapid alleviation of severe thyrotoxicosis. 

A typical chemical system is the oxidative decarboxylation of malonic acid catalyzed by cerium ions and bromine, the so-called Zhabotinsky reaction this reaction in a given domain leads to the evolution of sustained oscillations and chemical waves. Furthermore, these states have been observed in a number of enzyme systems. The simplest case is the reaction catalyzed by the enzyme peroxidase. The reaction kinetics display either steady states, bistability, or oscillations. A more complex system is the ubiquitous process of glycolysis catalyzed by a sequence of coordinated enzyme reactions. In a given domain the process readily exhibits continuous oscillations of chemical concentrations and fluxes, which can be recorded by spectroscopic and electrometric techniques. The source of the periodicity is the enzyme phosphofructokinase, which catalyzes the phosphorylation of fructose-6-phosphate by ATP, resulting in the formation of fructose-1,6 biphosphate and ADP. The overall activity of the octameric enzyme is described by an allosteric model with fructose-6-phosphate, ATP, and AMP as controlling ligands. 

First of all, the behavior of the enzymes in the membrane differs markedly from the behavior of the unbound enzymes in solution. It is pertinent to note that the medium in which the enzyme bound to a membrane acts might be determined not only by the composition and structure of the membrane itself, but also by the local concentration distribution of substrate and products. The microenvironment in the membranes is the result of a balance between the flow of matter and enzyme reactions. The substrate and product concentrations in the membrane differ from point to point across the membrane and also from those at the outer solution. By electron microscopy this was experimentally demonstrated beyond doubt with the DAB-peroxidase system by Barbotin and Thomas.16 The effects of these profiles were studied with... 

Isolation of the active species was reported and the spectral and physical properties support the 0=FeIV (Por) formulation.127 The Fe(IV)Por species are considered to be intermediates of peroxidase and catalase enzymic reactions. 

In another system, catalase or peroxidase enzymes can be used to produce an image in minute 02 bubbles (vesicular image) or an image in dye produced by the catalyzed reaction of a peroxy compound and a leuco dye, or a color developer in the presence of a dye-forming coupler. The enzymes are inactivated in areas exposed to light. In one system the metalloenzymes are poisoned by CN photodissociated by exposure of cyanotriphenylmethane compounds255 such as (123). 

Coupling of a second enzyme reaction HgOg+peroxidase - H20+oxidised peroxidase... 

CL detection is based on the optical emission of an excited species formed in a chemical reaction. For instance, an excited species is formed when luminol (or 3-aminophthalhydrazide) reacted with H202 as catalyzed by various substances, such as metal ions or the peroxidase enzyme. CL detection is achieved as in fluorescent detection, except that no excitation light is needed. 

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