Rhodobacter sphaeroides electron transfer from

Study the AG° dependence at different temperatures. This was done by Dutton and co-workers for the electron transfers from Bph to and Qa to (Bchl)2 in Rhodobacter sphaeroides photosynthetic reaction centers [139,140], which take place over about 13 A and 25 A, respectively [18], The rates were measured between 10 K and 300 K in series in which quinone substitutions provide AG° ranges of 0.5 eV and 0.8 eV for the two reactions respectively. The following conclusions were deduced from a thorough analysis of the experimental results ... 

Wang K, Zhen Y, Sadoski R, et al. Definition of the interaction domain for cytochrome c on cytochrome c oxidase. II. Rapid kinetic analysis of electron transfer from cytochrome c to Rhodobacter sphaeroides cytochrome oxidase surface mutants. / Biol Chem 1999 274 38042-50. 

Gunner, M. R., and Dutton, P. L., 1989, Temperature and -Delta-G-Degrees Dependence of the Electron-Transfer from Bph.- to Qa in Reaction Center Protein from Rhodobacter-Sphaeroides with Different Quinones As Qa J. Amer. Chem. Soc. Ill 3400n3412. 

Li, J. L., Gilroy, D., Tiede, D. M., and Gunner, M. R., 1998, Kinetic phases in the electron transfer from P+QA-QB to P+QAQB- and the associated processes in Rhodobacter sphaeroides R-26 reaction centers Biochemistry 37 2818n2829. 

Lin, X., Williams, J. C., Allen, J. P., and Mathis, P., 1994, Relationship between rate and free-energy difference for electron-transfer from cytochrome c(2) to the reaction center in Rhodobacter sphaeroides Biochemistry 33 13517913523. 

Table 2 Reaction of Ru-55-Cc with Rhodobacter Sphaeroides CcO mutants. The intracomplex rate constant A a for electron transfer from heme c to Cua, the dissociation constant K, and the second-order rate constant k2nd were at 5 mM, 45 mM, and 95 mM ionic strength, respectively, at pH 8 and 23...

Based on the nature of the cytochromes, there are two kinds of photosynthetic bacterial reaction centers. The first kind, represented by that of Rhodobacter sphaeroides, has no tightly bound cytochromes. For these reaction centers, as shown schematically in Fig. 2, left, the soluble cytochrome C2 serves as the secondary electron donor to the reaction center the RC also accepts electrons from the cytochrome bc complex by way ofCytc2- The rate of electron transfer from cytochrome to the reaction center is sensitive to the ionic strength of the medium. Functionally, cytochrome C2 is positioned in a cyclic electron-transport loop. In Rb. sphaeroides, Rs. rubrum and Rp. capsulata cells, the two molecules of cytochromes C2 per RC are located in the periplasmic space between the cell wall and the cell membrane. When chromatophores are isolated from the cell the otherwise soluble cytochrome C2 become trapped and held by electrostatic forces to the membrane surface at the interface with the inner aqueous phase. These cytochromes electrostatically bound to the membrane can donate electrons to the photooxidized P870 in tens of microseconds at ambient temperatures, but are unable to transfer electrons to P870 at low temperatures. 

In preparations from Rhodobacter sphaeroides which do not have a bound cytochrome low temperature electron transfer from P to Qa is reversible. This should also be the case in Rdp. viridis when the cytochromes are oxidised. We have therefore investigated the extent of reversible P oxidation at different redox potentials. In an oxidative titration reversible P formation is seen as the low potential haems are oxidised, it remains at a constant level from 50 to 250mV and then increases again as the high potential haems are oxidised and is lost as P is chemically oxidised. The reversible g=2.00 signal had the same line width and saturation characteristics at 100 and 380mV. The same result was obtained in both chromatophores and isolated reaction centres. 

Fig. 6.7 FTIR difference spectrum (light-minus-dark) of the absorbance changes associated with electron transfer from the special pair of bacteriochlorophylls (P) to a quinone (Qa) in photosynthetic reaction centers of Rhodobacter sphaeroides. The negative absorption changes result mainly from loss of absorption bands of P the positive changes, from the absorption bands of the oxidized dimer (P ). These measurements were made with a thin film of reaction centers at 100 K. The amplitudes are scaled arbitrarily. Adapted from [101]...

M. R. Gunner and P. L. Dutton, Temperature and -AG dependence of the electron transfer from Bph"" to Qa in reaction center protein from Rhodobacter sphaeroides with different quinones as Qa, / Am. Chem. Soc. Ill 3400 (1989). 

It is evident that the preceding considerations do not apply to all biological electron transfer systems. Even in the bacterial reaction center, the transfer between the two quinones Qa Qbj which takes place over 18 A [18], is characterized in Rhodobacter sphaeroides by a large entropic contribution, which has been attributed to the high solvent exposure of Qg [126]. By using the activation energy value reported in Ref. [126], two very different X values may be deduced from Eq. (23) = 0.1 eV and Aj = 2.5 eV. The previous considerations... 

On the planet Earth, the most important photoreaction occurs in green plants or in green or purple organisms. Their photochemical reaction centers contain a special pair of chlorins (cf. the purple bacterium Rhodobacter sphaeroides. Fig. 6.2). Solar photons cause electron transfer and generate a radical ion pair. Within two picoseconds, the negative charge is transferred to a second chlorin, and from it to a quinone. ... 

Fig. 25. Electron transfer pathways in the RC isolated from Rhodobacter Sphaeroides strain R-26. (BChl)2 is dimer of the bacterioehlorophyll, BPh is the bacteriopheophytin, Q, -ubiquinone. The electron transfer rates are for the native RC with ubiquinone —10 as Q,v at room temperature. The rates given in parenthesis were determined below 100 K [194-197]...

Kinetics of Electron Transfer in RC Protein from Rhodobacter Sphaeroides... 

Figure 2. The ligand common to all molybdenum and tungsten enzymes, MPT, is shown here in several formats (a) in common stick notation (b) as a ball and stick (c) an orientation rotated 90° from view (b) to emphasize the spacial relationship between the pterin plane and the dithiolene-pyran ring portion (d) MGD in common stick notation and for comparison, (e ) FAD, a common electron-transfer prosthetic group. Coordinates for the views in (b) and (c) are taken from the data deposited in the Protein Data Bank (PDB) for the 1.3-A resolution structure of DMSO reductase from Rhodobacter sphaeroides.

The X-ray crystal structure of a reaction centre from Rhodobacter sphaeroides with a mutation of tyrosine M210 to tryptophan (YM210W) has been determined to have a resolution of 2.5 A (McAuley et al., 2000). It is shown that the main effect of the introduction of the bulkier tryptophan in place of the native tyrosine is a small tilt of the macrocycle of the (Bchl)L. The effect of the redox potential of the electron acceptor (Bchl) in RC from Rb. spheroides on the initial electron transfer rate and on the P (Bchl) population was investigated (Sporlein et al., 2000). Analysis of experimental... 

Nabedryk, E., Breton, J., Okamura, M.Y., and Paddock, M. L. (2001) Simultaneous replacement of Asp-L210 and Asp-M17 with Asn increases proton uptake by Glu-L212 upon first electron transfer to Qb in reaction centers from Rhodobacter sphaeroides, Biochemistry 40, 13826-13832. 

Gunner, M. R. (1988). The temperature and — AG dependence of long range electron transfer in reaction center protein from Rhodobacter sphaeroides. U niv. of Pennsylvania, Philadelphia. 

Initial electron transfer in the reaction center from Rhodobacter sphaeroides. Proc. NaU. Acad. Sci USA, 87 5168fi5172. 

Lin, S., Taguchi, A. K. W., and Woodhury, N. W., 1996, Excitation wavelength dependence of energy-transfer and charge separation in reaction centers from Rhodobacter-sphaeroides -evidence for adiabatic electron-transfer. J. Rhys. Chem., 100 17067nl7078. 

Streltsov, A. M., Yakovlev, A. G., Shkuropatov, A. Y., and Shuvalov, V. A., 1996, Femtosecond kinetics of electron transfer in the bacteriochlorophyll-M-modified reaction centers from Rhodobacter sphaeroides (R-26). FEES Letts., 383 129nl32. 

The formation of a hydrogen bond between the amide proton and one carbonyl oxygen of NQ was indicated in the Ec + —NQ /M" complex to stabilize the complex (see above). Electron-transfer reactions were believed to be regulated through such noncovalent interactions that play an important role in biological ET systems, where electron donors and acceptors are usually bound to proteins at a fixed distance (123-127). Eor example, in the bacterial photosynthetic reaction center (bRC) from Rhodobacter Rb) sphaeroides, an electron is transferred from... 

Fig. 9. (A) Absorption spectrum of Rb. sphaeroides used as a reference to show the Qx and Qy bands of the primary donor (P), BChl [B] and bacteriopheophytin [BO] (B) Femtosecond absorption changes at 920 (a), 785 (b) and 545 nm (c) vs. the delay time of the monitoring pulse measured at room temperature, and (C) absorption changes at 920 (a) and 794 nm (b) measured at 25 K. Figure source (A) see Fig. 7 (B) Holzapfel, Finkele, Kaiser, Oesterheldt, Scheer, Stilz and Zinth (1990) Initial electron transferin the reaction center from Rhodobacter sphaeroides. Proc Nat Acad Sci, USA 87 5170 (C) Zinth and Kaiser (1993) Time-resolved spectroscopy of the primary electron transfer in reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis. I n JR Norris and J Deisenhofer (eds) The Photosynthetic Reaction Center, Voi il, p 82. Acad Press.

W Holzapfel, U Finkele, W Kaiser, D Oesterheldt, H Scheer, HU Stilz and WZinth (1990) Initial electron transfers the reaction center from Rhodobacter sphaeroides. Proc Nat Acad Sci, USA 87 5168-5172... 

C Lautwasser, U Finkele, H Scheer and WZinth (1991) Temperature dependence of the primary electron transfers photosynthetic reaction centers from Rhodobacter sphaeroides. Chem Phys Lett 183 471-477... 

Figure 2. Arrangement of the electron transfer cofactors in the photosynthetic reaction center protein from the bacterium Rhodobacter sphaeroides. The figure shows the special pair of bacteriochlorophylls (top, in green and light blue), two accessory bacteriochlorophyll molecules (dark blue), two bacteriopheophytins (red), the primary quinone (Qa), the secondary quinone (Qb), and the non-heme iron.

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