Kinetic phases in the electron transfer from P{sup +}Q{sub A}{sup -}Q{sub B} to P{sup +}Q{sub A}Q{sub B}{sup -} and the associated processes in Rhodobacter sphaeroides R-26 reaction centers.
Electron transfer from P{sup +}Q{sub A}{sup -}Q{sub B} to form P{sup +}Q{sub A}Q{sub B}{sup -} was measured in Rhodobacter sphaeroides R-26 reaction centers (RCs) where the native primary quinone, ubiquinone-10 (UQ{sub A}), was replaced by 2-methyl-3-phytyl-1,4-naphthoquinone (MQA). The native secondary quinone, UQ-10, was retained as UQ{sub B}. The difference spectrum of the semiquinone MQ{sub A}- minus UQ{sub B}- absorption is very similar to that of MQ- minus UQ- in solution (398-480 nm). Thus, the absorption change provides a direct monitor of the electron transfer from MQ{sub A}- to UQ{sub B}. In contrast, when both Q{sub A} and Q{sub B} are UQ-10 the spectral difference between UQ{sub A}- and UQ{sub B}- arises from electrochromic responses of RC chromophores. Three kinetic processes are seen in the near UV (390-480 nm) and near-IR (740-820 nm). Analysis of the time-correlated spectra support the conclusion that the changes at {tau}{sub 1} {approx} 3 {micro}s are mostly due to electron transfer, electron transfer and charge compensation are mixed in {tau}{sub 2} {approx} 80 {micro}s, while little or no electron transfer occurs at 200-600 {micro}s ({tau}{sub 3}) in MQAUQB RCs. The 80-{micro}s rate has been previously observed, while the fast component has not. The fast phase represents 60% of the electron-transfer reaction (398 nm). The activation energy for electron transfer is {Delta}G {approx} 3.5 kcal/mol for both {tau}{sub 1} and {tau}{sub 2} between 0 and 30 C. In isolated RCs with UQ{sub A}, if there is any fast component, it appears to be faster and less important than in the MQ{sub A} reconstituted RCs.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- ER
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 938129
- Report Number(s):
- ANL/CHM/JA-27277; TRN: US200906%%423
- Journal Information:
- Biochemistry, Vol. 37, Issue 9 ; Mar. 3, 1998
- Country of Publication:
- United States
- Language:
- ENGLISH
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