2.6- dichlorophenolindophenol

The stoichiometry and the rate law for the oxidation by alkaline ferricyanide are, respectively (EDTA = H4Y)  

An irreversible outer sphere electron transfer is thought to be the most likely ratedetermining step in view of the lack of retardation by Fe(CN)6 and CN ions. 

Sixteen other nitrogen-containing chelates were examined by Lambert and Jones , and a very good correlation is observed between E and AS indicating a single effect to predominate in all instances. 

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Chemical Properties. The most significant chemical property of L-ascorbic acid is its reversible oxidation to dehydro-L-ascorbic acid. Dehydro-L-ascorbic acid has been prepared by uv irradiation and by oxidation with air and charcoal, halogens, ferric chloride, hydrogen peroxide, 2,6-dichlorophenolindophenol, neutral potassium permanganate, selenium oxide, and many other compounds. Dehydro-L-ascorbic acid has been reduced to L-ascorbic acid by hydrogen iodide, hydrogen sulfide, 1,4-dithiothreitol (l,4-dimercapto-2,3-butanediol), and the like (33). 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

Dipping solution Dissolve 40 mg 2,6-dichlorophenolindophenol sodium in too ml ethanol. 

Although the first purification of bNOS was a monomer, it is now clear that the enzyme in all cases is effective as a dimer. A purified macrophage iNOS was used by Baek and coworkers98 to separate the holoenzyme from the monomers. The subunits do not have NOS activity but do have the ability to oxidize reduced triphosphopyridine nucleotide with either ferricyanide, cytochrome c or dichlorophenolindophenol. When all of the missing factors are present, but not when any is missing, the authors find recombination, as shown in Figure 13. 

Seasonal Study of Mixed Function Oxidases.— A seasonal study of hepatic microsomal mfo components has been conducted in female R and S fish (submitted for publication). Components studied were cytochromes P-450 and 5, NADPH-cytochrome c reductase, NADPH-dichlorophenolindophenol reductase, NADH-cytochrome c reductase and NADH-cytochrome 5 reductase. All were monitored at 30°C by standard spectrophotometric methods following optimization procedures (8, 9 > 10, n, J 2). Microsomal and total hepatic protein (137 and liver weight to body weight ratios were also monitored. 

Additionally, Wang and Watt have shown that the FeMo protein alone can act as an uptake hvdrogenase(63). Specifically, H2 in the presence of [FeMo] causes the reduction of oxidizing dyes such as methylene blue or dichlorophenolindophenol in the absence of Fe protein. The hydrogen evolution and uptake behavior of nitrogenase proteins forces us to consider the ways in which hydrogen can interact with transition metal sulfur centers. This we discuss in the following section. 

Selected entries from Methods in Enzymology [vol, page(s)] Electron-transport chain [components, 69, 205, 206 sites of inhibition, 69, 676, 677] chloroplast [autoxidizable carriers, 69, 416, 417 DBMIB, 69, 422, 423 dichlorophenolindophenol and related carriers, 69, 418 ferricyanide, 69, 417, 418 isolated, 69,... 

The enzyme was found to be unstable in soluble form and to bind FAD tightly with a K of 61 pM. Its selectivity for an acceptor of electrons was demonstrated by its failure to reduce ferricyanide, dichlorophenolindophenol, methylene blue, or cytochrome c (directly). Tantalizingly the loss of activity was nearly immediate in the presence of ATP, prompting the suggestion that ATP may be a physiological regulator of the activity of the enzyme. Activity was stimulated by dithiothreitol at low concentrations and loss of activity was stimulated by salts and EDTA. 

Because of the clinical significance of vitamin C, it is essential to In-able to detect and quantify its presence in various biological materials. Ana lytical methods have been developed to determine the amount of ascorbic acid in foods and in biological fluids such as blood and urine. Ascorbic acid may be assayed by titration with iodine, reaction with 2,4-dinitrophenylhy-drazine, or titration with a redox indicator, 2,6-dichlorophenolindophenol (DCIP) in acid solution. The latter method will be used in this experiment because it is reasonably accurate, rapid, and convenient and can be applied to many different types of samples. 

Electron mediators are usually organic molecules that are redox active, such as ferrocene derivatives, benzoquinone, N-methylphenazium, and 2,6-dichlorophenolindophenol (DCPIP). Ferricyanide has also been used as an electron mediator. They offer the advantages of non-... 

The oxidation of the enamine on El in PDHc by nonlipoic acid acceptors has also been explored for many years. For example, ferricyanide reduction monitored by visible spectroscopy has become a standard test to assay El activity, notwithstanding the attendant problems, including the instability of the thiazolium ring to such conditions. 2,6-Dichlorophenolindophenol (DCPIP) has also been used as an alternative electron acceptor in mechanistic studies of PDHcs75. 

In addition to transfer of hydrogen between various nicotinamide nucleotides, the transhydrogenases from Pseudomonas 17), spinach 11, 13), and Azotobacter 9, 19) also catalyze a diaphorase reaction, using either NADH or NADPH plus an artificial acceptor, e.g., potassium fer-ricyanide or dichlorophenolindophenol. As expected, 2 -AMP stimulates the NADH-linked diaphorase reaction catalyzed by the Pseudomonas enzyme 17). 

The turnover number at infinite concentration of both substrates with dichlorophenolindophenol as acceptor is virtually identical with that with cytochrome c at the same pH, though the pH optimum for dichlorophenolindophenol may not be the same (386). The reductase is also very... 

Dichlorophenolindophenol choline dehydrogenase and, 261 cytochrome 6j and, 267 cytochrome P-450 reductase and, 167 a-glycerophosphate dehydrogenase and,... 

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