Binding sites, electron transfer process

When metallo-enzymes effect the oxidation or reduction of organic substrates or simple molecules such as H2O, N2 or O2, they often function as multielectron donors or acceptors with two or more metals at the active site. The electronic coupling between the metals is often accompanied by unique spectroscopic features such as electron spin-spin coupling. The metal-metal electronic coupling may facilitate the multi-electron-transfer reactions with the substrates. In simpler molecular systems, two electron-transfer processes most often require substrate binding , as in an inner-sphere, group (or atom ) transfer process. ... 

While Fe(SCys)4, [2Fe-2S], [3Fe-4S] and [4Fe-4S] clusters all function as one-electron donors or acceptors, the more complex double-cubane [8Fe-7S] cluster that is found only in nitrogenases (see Nitrogenase Catalysis Assembly) has the potential to mediate two-electron transfer processes.Three methods have been employed to functionalize Fe-S centers for substrate binding and activation. The first involves having an accessible Fe coordination site as in the mononuclear Fe centers of nitrile hydratase and SOR, and the [4Fe-4S] clusters at the active sites of hydratases/dehydratases and radical-5-adenosylmethionine (SAM) enzymes.Indeed the recent recognition of the importance of the superfamily of radical-SAM enzymes in initiating radical reactions, via cluster-mediated reductive cleavage of SAM to yield a... 

The prospect of advancing chemical sensor technology, modelling electron-transfer processes in biological systems and producing new redox catalysts has led to considerable interest in the design and syntheses of redox-active macrocyclic receptor molecules that contain a redox centre in close proximity to a host binding site. ... 

The properties of electron transfer proteins that are discussed here specifically affect the electron transfer reaction and not the association or binding of the reactants. A brief overview of these properties is given here more detailed discussions may be found elsewhere (e.g.. Ref. 1). The process of electron transfer is a very simple chemical reaction, i.e., the transfer of an electron from the donor redox site to the acceptor redox site. 

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