Intramolecular LRET

Two features of the intramolecular LRET in azurins deserve attention. The first is that the copper site is characterized by an exceptionally low Frank-Condon barrier for electron transfer (14, 20). The second is that the Cys3-Cys26 disulfide bridge plays, most probably, only a structural role in this protein (20). Hence, the LRET induced from RSSR to the Cu(II) center is... 

Summarizing the results of studies of intramolecular ET in azurins, it is important to stress that in all probability, the induced ET between the disulfide radical and the blue copper(II) center is not part of any physiological function, and the role of the disulfide is stmctural, solely. Still, azurin has turned out to be a very useful model system for examination of different parameters controlling LRET rates in proteins. The impact of specific stmctural changes introduced by single-site mutations has been studied in order to obtain a better understanding... 

Intramolecular ET between distinct copper centers is part of the catalytic cycles of many copper-containing redox enzymes, such as the multicopper oxidases, ascorbate oxidase, and ceruloplasmin, as well as the copper-containing nitrite reductases. Examination of internal LRET in these proteins is of considerable interest as it may also provide insights into the evolution of selected ET pathways in particular, whether and how the enzymes have evolved in order to optimize catalytic functions. With the increase in the number of known high-resolution 3D structures of transition metal containing redox enzymes, studies of structure-reactivity relationships have become feasible and indeed many have been carried out during the last two decades. 

AU three T1 centers are well protected from the solvent by the protein matrix. Thus, it is not surprising that only indirect copper reduction by radicals via the exposed disulfide groups is observed (72). In fact, this behavior is reminiscent of results of our studies of intramolecular ET in azurins where, in addition to the direct, bimolecular reduction of both the disulfide group and the T1 site, LRET takes place from the disulfide radical to Tl(Cu ) over a distance of 2.6 nm... 

The semiclassical Marcus equation can be applied to electron transfer between spatially fixed and oriented redox centers (26). Values obtained by employing this theoretical framework are in good agreement for both wild type and single-site mutants of Pae azurin (15), thus supporting the applicability of this analysis of the LRET process. The mechanism of intramolecular electron transfer through matrices of biological macromolecules, mainly proteins, has attracted considerable current interest (25). Moreover, the question of whether... 

Comparison of the kinetic LRET data presented for the Trp -Tyr redox pair (cf Figure 1) with those for intramolecular electron transfer across the same... 

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