Redox multicenter

Multicenter Molecules with Non-interacting Redox Centers... 

High-resolution X-ray structures are now available for several multicenter ET proteins [6-9], as well as for redox protein-protein complexes [10-12]. These... 

Cytochrome C4 A Prototype for Microscopic Electronic Mapping of Multicenter Redox Metalloproteins... 

The usage of the molecular orbital version of the Lewis definitions allows to discuss donor and acceptor interactions, involving delocalized electron systems and locahzed but multicentered bonds. Moreover, one can take into account all degrees of electron donation ranging from nearly zero in the case of weak intermolecular attractions and idealized ion association, to complete transfer of one or more electrons (redox). 

Electron-transfer (ET) reactions play a central role in all biological systems ranging from energy conversion processes (e.g., photosynthesis and respiration) to the wide diversity of chemical transformations catalyzed by different enzymes (1). In the former, cascades of electron transport take place in the cells where multicentered macromolecules are found, often residing in membranes. The active centers of these proteins often contain transition metal ions [e.g., iron, molybdenum, manganese, and copper ions] or cofactors as nicotinamide adenine dinucleotide (NAD) and flavins. The question of evolutionary selection of specific structural elements in proteins performing ET processes is still a topic of considerable interest and discussion. Moreover, one key question is whether such stmctural elements are simply of physical nature (e.g., separation distance between redox partners) or of chemical nature (i.e., providing ET pathways that may enhance or reduce reaction rates). 

It is of interest to compare rate constants and activation parameters of the intramolecular ET in Ps-NiR with those determined for analogous intramolecular ET processes in other multicentered redox enzymes. Reversible intramolecular ET reaction between type 1 and 2 sites in the copper-containing nitrite reductases (CuNiR isolated from A. xylosoxidans and A. cycloclastes)... 

The above results provide some insights into the intricate control that may operate in internal ET processes in multicenter redox enzymes. Specifically, it is of interest to compare control mechanisms exerted on sites that function only in mediating ET (e.g., T1 or Cua sites) with those that function as catalytic centers, that is, sites that interact with substrates (dj-heme, T2 sites). Indeed, while the former centers are characterized by relatively low reorganization energies, the latter have relatively high ones. 

Several Mo-containing enzymes are known to occur in various organisms (Table 4.1). All these molybdoenzymes are multicenter electron-transfer proteins, with the Mo moiety serving as both substrate binding site and redox site. Stiefel, Coucouvanis, and Newton (1993) have reviewed Mo enzymes in detail. 

Leger C, Lederer F, Guigliarelli B, Bertrand P. Electron flow in multicenter enzymes theory, applications, and consequences on the natural design of redox chains. J Am Chem... 

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