Electron Transfer Routes

The remote site on plastocyanin consists of acidic residues 42-45 and 59-61 on either side of Tyr 83. Typically, positively charged complexes react —50% at this site. Evidence has been obtained for cytochrome c (97) and cytochrome f(35) reacting more extensively (possibly exclusively) at this site. 

The X-ray crystal structure of ascorbate oxidase (21) defines a route for electron transfer from the T3qie 1 Cu center to the Cus site via connecting Cys and His residues. The Type 1 domain has structural 

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Let us return to Scheme 6.10 and consider the fate of the diphenylalkyl carbinol formed. The carbinol is optically active, and a configuration inversion takes place partially. Obviously, a dual reactivity is observed. Accordingly, the electron-transfer route can be represented by Scheme 6.12. 

Under anaerobic conditions with a low partial pressure of hydrogen and under low intensity illumination, hydrogen evolution takes place and the overall reaction can be represented by (2.4.1) [172] the electron transfer route is as follows [141] ... 

Blue copper proteins, 36 323, 377-378, see also Azurin Plastocyanin active site protonations, 36 396-398 charge, 36 398-401 classification, 36 378-379 comparison with rubredoxin, 36 404 coordinated amino acid spacing, 36 399 cucumber basic protein, 36 390 electron transfer routes, 36 403-404 electron transport, 36 378 EXAFS studies, 36 390-391 functional role, 36 382-383 occurrence, 36 379-382 properties, 36 380 pseudoazurin, 36 389-390 reduction potentials, 36 393-396 self-exchange rate constants, 36 401-403 UV-VIS spectra, 36 391-393 Blue species... 

Tanaka and co-workers (2000) reported that the NO) nitration of 1,8-dimethylnaph-thalene leads to 2-nitro and 4-nitro products. For the 2-nitro products, the reaction proceeds as electrophilic substitution The nitro group comes into the ipso position and then migrates to position 2, thus giving the final product. For the 4-nitro product, the process develops according to the electron-transfer route. The spin density of the 1,8-dimethylnaphthalene cation radical is highest at position 4 (or the same at position 5). It is the para nitration that takes place in the experiment. 

Deactivation of an excited species can proceed through radiation or radiationless decays, energy transfer quenching, or electron transfer routes. The operation of artificial photosynthetic devices relies mainly on electron-transfer (ET) processes induced by an excited species [16, 17]. Two general mechanisms can be involved in the ET process of an excited species Reductive ET quenching of an excited species, S, by an electron donor D, results in the redox products S- and D+ (Fig. 4 a). Alternatively, oxidative quenching of the excited species by an electron acceptor, A, can occur (Fig. 4b), resulting in the electron transfer products S+ and A-. 

Figure 14 Similarity between the putative electron-transfer routes to and from the type 1 copper sites in plastocyanin and nitrite reductase. (Reproduced with permission of Chapman and Hall from J. Sanders-Loehr, in Bioinorganic Chemistry of Copper , ed. K.D. Karlin and Z. Tyeklar, 1993, p. 51) ...

UV-VIS Spectra Reduction Potentials Active-Site Protonations Charge on Proteins Self-Exchange Rate Constants Electron Transfer Routes Comparison with Rubredoxin Summary References... 

The available results demonstrate readily the complementarity of the kinetic and thermodynamic data obtained from stopped-flow, UV-Vis, electrochemical and density measurements, and yield a mutually consistent set of trends allowing further interpretation of the data. The overall reaction volumes determined in four different ways are surprisingly similar and underline the validity of the different methods employed. The volume profile in Fig. 1.20 illustrates the symmetric nature of the intrinsic and solvational reorganization in order to reach the transition state of the electron-transfer process. In these systems the volume profile is controlled by effects on the redox parmer of cytochrome c, but this does not necessarily always have to be the case. The location of the transition state on a volume basis is informative regarding the early or late nature of the transition state, and therefore details of the actual electron-transfer route followed. 

However, to our knowledge, this reaction has not been clearly validated. Reaction of a pre-prepared cation radical with the cyanide ion may also take place by the electron-transfer route of reactions 7 and 8. 

Figure 7-2 Re-reduction of bacterial cytochrome c peroxidase. Yeast cytochrome c peroxidase is a monoheme enzyme which is oxidized by hydrogen peroxide to yield a ferryl iron and a protein cation radical. Two electrons are required for re-reduction. The two-domain cytochrome c peroxidases contain a peroxidatic (P) heme and an electron transfer (E) heme. The state shown is at the end of a catalytic cycle and contains two oxidizing equivalents, one on the P heme (as Fe(IV)) and one on the E heme (as Fe(III)). Re-reduction of the enzyme could proceed via (1) a successive pair of electron transfers at the E heme with the first of the electrons passing to the P heme, (2) two separate electron transfer routes, or (3) a single electron transfer route which diverges within the protein.

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