Proteins, redox

Such free radicals may be stabilized by binding to proteins. Redox reactions may also occur between ionic species, for example the oxidation of reduced cytochrome c by hexacyanoferrate (ferricyanide) ions. 

A variety of physical methods has been used to ascertain whether or not surface ruthenation alters the structure of a protein. UV-vis, CD, EPR, and resonance Raman spectroscopies have demonstrated that myoglobin [14, 18], cytochrome c [5, 16, 19, 21], and azurin [13] are not perturbed structurally by the attachment of a ruthenium complex to a surface histidine. The reduction potential of the metal redox center of a protein and its temperature dependence are indicators of protein structure as well. Cyclic voltammetry [5, 13], differential pulse polarography [14,21], and spectroelectrochemistry [12,14,22] are commonly used for the determination of the ruthenium and protein redox center potentials in modified proteins. 

Flash photolysis and pulse radiolysis techniques have been developed to study Fe Ru ET in Ru-modified proteins [21,26,27]. A method that allows study of electron transfer from a surfaee ajRu(IIIXhistidine) to a protein redox center is outlined in the Scheme [21]. The ET reaction is initiated by photogenerated... 

Protein Redox Centers Involved Initiating Mode Kt S Distance A AE Volts Ref. 

Stimulation of N-methyl-D-aspartate (NMDA) receptors (see Chapter 16) in the nervous system is linked to activation of NO synthase and creation of an intracellular NO signal (Yun et al., 1998). NO can directly activate Ras protein redox modification of Ras protein is assumed to take place in this process. 

Aslund, E, Bemdt, K.D., Holmgren, A. Redox potentials of glutaredoxins and other thiol-disulfide oxidoreductases of the thioredoxin superfamily determined by direct protein-protein redox equilibria. J Biol Chem 272(49), 30780-30786 (1997)... 

Dalle-Donne I, Rossi R, Giustarini D, Colombo R, Milzani A. 2007. S-glutathionyla-tion in protein redox regulation. Free Radic Biol Med 43 883-898. 

In this paper we focus on two prototypic protein redox couples, cytochrome (e)e/cytochrome b (b,.) and c/cytochrome c peroxidase (ccp) which have been the subjects of detailed studies in our labs. 

Figure 2 Electron transfer series in native and synthetic model clusters of the Fe4S4 center in the Fe-protein. Redox potential versus NHE, Fe Mossbauer isomer shift (S at 4.2 K vs. iron), mean iron oxidation state, and spin state are indicated for each redox state. Syntheses and ligand-substitution reactions are indicated for synthetic clusters...

Although the ET processes represented by reactions 3 and 5 are nonphysiologi-cal, they can provide useful information. Thus, by varying the structure of the flavin it is possible to probe the steric and electrostatic environment of a protein redox center [38, 39]. This can be used as a method for assessing functional relationships between members of a homologous series of redox proteins (kinetic taxonomy). It is also possible to use these reactions to test the functional integrity of a redox center in a site-specific mutant [43]. 

Reduction of horse cytochrome C with [Colsepll ", [Co(diAMsar)]2+, and [Co(NOcapten)]2+ cations was reported in Refs. 316-320. The intrinsic reactivity of these complexes with proteins make it possible the use of clathrochelates as potential protein redox titrants, electrochemical mediators, and electrode modifiers. 

Relatively simple syntheses for the majority of macrobicyclic complexes, compared with conventional techniques for the preparation of macrocyclic compounds, have made such complexes attractive not only for research, but also for practical application as electron carriers, catalysts for electro- and photochemical processes, and some other purposes (e.g., protein redox titrants, biological electrochemical mediators, and ionophore and electrode modifiers). 

Redox-proteins usually lack direct electrical contact with electrodes because the redox site is embedded in the protein. This situation insulates the electrical communication between the redox-site and the electrode by the spatial separation of the protein redox-site from the electrode support. Suitable func-... 

Since the electrode and the protein redox center may be considered as a donor-acceptor pair, the distance, or spatial, separation of the enzyme redox center from the electrode by means of the protein shell prohibits the direct electrical communication between the redox site and the electrode. Substantial research efforts were directed during the last two decades to overcome the insulating protein barrier surrounding the redox centers and... 

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