Biological redox processes

Many model studies have focused on methaemerythrin, i.e. the oxidized Fe(III)-Fe(III) form of haemerythrin which contains an 0x0 (rather than hydroxy) bridge. Methaemerythrin does not bind O2, but does interact with ligands such as [N3] and [SCN]. Reaction 28.8 makes use of the trispyrazolylborate ligand, [HBpz3] , to model three His residues the product (28.14) contains antiferro-magnetically coupled Fe(III) centres. 

Oxygenases are enzymes that insert oxygen into other molecules a monooxygenase inserts one oxygen atom, and a dioxygenase inserts two. 

The active site in a cytochrome P-450 is a haem unit, and structural data for cytochrome P-450 complexed with 

The insertion of O into the C—H bond of RH is thought to involve a radical pathway. 

In this section we look at ways in which Nature carries out redox chemistry with reference to blue copper proteins, iron-sulfur proteins and C5fiochromes the redox steps in Photosystem II were outlined in the discussion accompanying equation 21.53. We have already discussed two topics of prime importance to electron transfer in Nature. The first is the way in which the reduction potential of a metal redox couple such as Fe /Fe + can be tuned by 

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Nowadays, studies of direct electrochemistry of redox proteins at the electrodesolution interface have held more and more scientists interest. Those studies are a convenient and informative means for understanding the kinetics and thermodynamics of biological redox processes. And they may provide a model for the study of the mechanism of electron transfer between enzymes in biological systems, and establish a foundation for fabricating new kinds of biosensors or enzymatic bioreactors. 

Other biological redox processes are for instance important in the bacterial degradation of chemical products found in the soil (such as the oxygenases illustrated in Chapter 9, Section 1.1). 

As electrochemistry is particularly suitable for studying electron transfer events, its application to biological redox processes appears reasonable. Unfortunately, the difficulties encountered and the few results obtained until the beginning of the 1980s meant that it became firmly believed that it would not be possible to use this technique to study the direct electron transfers activated by proteins. The basis of this scepticism were the following ... 

In part motivated by the desire to model biological redox processes, there have been many studies in which Robson-type macrocycles (205) (R = H) have been employed to form dinuclear manganese species.For example, a novel macrocyclic heterodinuclear catalase-like model complex of type (206) has been reported. " This complex can dismute hydrogen peroxide to dioxygen in basic aqueous solution. 

Since the initial observation of flavin radical species by Michaelis and coworkers the involvement of flavins in one-electron oxidation-reduction processes in biological systems has occupied the attention of workers in the field of redox enzymology up to the present time. Flavin coenzymes occupy a unique role in biological oxidations in that they are capable of functioning in either one-electron or two-electron transfer reactions. Due to this amphibolic reactivity, they have been termed in a recent review to be at the crossroads of biological redox processes. 

Radiation chemistry, and pulse radiolysis in particular, is now a mature subject that is available as a very valuable and a powerful tool by which fundamental problems in free radical reaction mechanisms can be addressed. This chapter is restricted to studies concerning sulfur-centered radicals and radical-ions performed by radiation chemistry techniques in the first eight years of XXI century (2001-2008). SuMur-centered radicals represent a very interesting class of radicals since they exhibit very interesting redox chemistry, including biological redox processes, and different spectral and kinetic properties as... 

The following sections will concentrate on the analytical application of redox proteins and redox enzymes for biosensing. The biomolecule will be briefly introduced, the major route for its direct electric contact to electrodes outlined and the analytical application discussed. The bioelectrochemical studies on structure-function relationship and their role in biological redox processes will not be covered in detail in this review. 

Metal storage and transport Dealing with O2 Biological redox processes... 

The potential of pulse radiolysis for studying biological redox processes, particularly of macromolecules, was recognized rather early. It was initially employed for investigating radiation-induced damage and, later on, as an effective tool for resolving electron transfer processes to and within proteins. Cytochrome c, a well-characterized electron-mediating protein, was the first to be... 

Under electrochemical conditions, electrons are added to (reduction) or withdrawn from (oxidation) a molecule or ion of interest at an electrode surface and the consequences of that process are followed by means of many electrochemical, spectral, and other techniques. Naturally, there is no assurance that the redox pathways and mechanisms developed on the basis of electrochemical experiments will bear any relationship to biological redox pathways. Nevertheless, there is now a small but significant body of evidence which supports the view that redox mechanisms deduced for small organic biomolecules using purely electrochemical techniques do give rather unique insights into biological redox processes. 

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