Protein electrochemical reduction

The Cu11 atoms are well separated and are not coupled magnetically, but absorb intensely (3800 1 mol-1 cm-1 at 635 nm) in the visible region. This charge-transfer absorption is reversibly lost on electrochemical reduction and regained on reoxidation by 02. These properties, together with A hyperfme coupling apparent in the ESR spectrum, are closely related to those of the distorted tetrahedral type-1 Cu site of blue Cu proteins,310 despite the different Cu coordination stereochemistry in the cluster. 

Disulfides — A disulfide bond (R-S-S-R) is a strong covalent bond formed by the oxidation of two sulfhydryl groups (R-S-H). An amino acid that commonly forms S-S bonds in proteins is cysteine. When two cysteines are bonded by an S-S bond, the resulting molecule between the two protein chains is called cystine. The presence of disulfide bonds helps to maintain the tertiary structure of the protein. Industrial production of L-cysteine is based on the electrochemical - reduction of L-cystine in acidic - electrolytes using lead or silver -> cathodes. 

UV photolysis of CpMn(CO)3 in toluene leads to loss of CO and formation of CpMn(CO)2( ] -toluene). Kinetic studies suggest that the binding energy of the toluene is ca. 60kJmor. The binding of H2 to CpMn(CO)2 has been studied in supercritical CO2 solvent. It has been proposed that pyrylium and pyridinium salts such as (35) can be used to label proteins and thereby aid in the detection and characterization of receptor sites. Cymantrene bound to lysine residues of bovine serum albumin (BSA) has been used as a redox label. Electrochemical reduction of the label established an impressive BSA detection limit of 2 x 10 M. 

Direct electrochemistry has also been used (72-78) to couple the electrode reactions to enzymes for which the redox proteins act as cofactors. In the studies, the chemically reduced or oxidized enzyme was turned over through the use of a protein and its electrode reaction as the source or sink of electrons. In the first report (72, 73) of such application, the electrochemical reduction of horse heart cjd,ochrome c was coupled to the reduction of dioxygen in the presence of Pseudomonas aeruginosa nitrite reductase/cytochrome oxidase via the redox proteins, azurin and cytochrome C551. The system corresponded to an oxygen electrode in which the four-electron reduction of dioxygen was achieved relatively fast at pH 7. 

Cysteamine was used to couple redox-active carboxylalkyl-4,4 -bipyridinium salts to the gold surface . The nonordered monolayer assembly was then transformed into a densely packed monolayer with 1-hexadecanethiol and cyclic voltammetry of the surface bound viologen was performed. The electron transfer rate constants to the bipyridinium sites depended on the alkyl chain length Abridging the redox site to the electrode. Electron transfer rate constants followed the Marcus theory. Cysteic-acid-active ester monolayers chemisorbed on gold were used to electrode-immobilize the protein glutathione reductase, then a bipyridinium carboxylic acid was condensed onto the enzyme in the presence of urea to wire the protein towards electrochemical reduction (Figure 6.26). 

Several co-oxo fatty acids are transformed to the corresponding a,co -dicarboxylic acids, whereas -formylesters of fatty acids are decarboxylated to the co-hydroxy fatty acids and carbon dioxide1111. For several co-oxo fatty acids turnover frequencies (measured as O2 consumption) between 1.8 to 25 s 1 were found. Many P450 systems are multi-component enzymes with small protein cofactors such as putidaredoxin performing the electron mediation between NAD(P)H and the active site of the enzyme. Vilker and coworkers recently were able to show that NADPH can be omitted from the catalytic cycle by direct electrochemical reduction of putidar-... 

The possibility of electrochemical reduction and oxidation of cytochrome c on a gold electrode was demonstrated by means of spectroelectro-chemical measurements. The measurements were made in a cell with an optically transparent (grid) electrode, thus permitting the spectra to be recorded directly during electrochemical measurements. Figure 8 shows the spectra of the electrochemically reduced (curve 1) and oxidized (curve 2) cytochrome c. The spectra of ferro- and ferricytochrome c obtained electrochemically are identical with those of the chemically reduced and oxidized forms of cytochrome c. Investigations have also shown that after electrochemical reduction of the protein its enzymatic activity is preserved. ... 

The direct electrochemical reduction and oxidation of bacteriorhodopsin, a bacterial photoreceptor protein, have recently been described. The redox site of this molecule is organic, being a conjugated double bond system and a Schiff base. As previously noted for other proteins, strong adsorption onto mercury is evident with bacteriorhodopsin. The adsorbed molecules undergo reduction-oxidation reactions near -0.8 V which appear to be polarographically reversible. An oxidation wave is observed at platinum at +0.80 V and has been ascribed to the chromophore. ... 

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