Temperature and minus. Delta. G degree dependence of the electron transfer from BPh sup sm bullet minus to Q sub A in reaction center protein from Rhodobacter sphaeroides with different quinones as Q sub A

Journal Article · Wed Apr 26 00:00:00 EDT 1989 · Journal of the American Chemical Society; (USA)

DOI:https://doi.org/10.1021/ja00191a043· OSTI ID:5132065

Gunner, M R; Dutton, P L ^[1]

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1. Univ. of Pennsylvania, Philadelphia (USA)

The rate of electron transfer from BPh{sup {sm bullet}{minus}} to Q{sub A} (k{sub 1}) was determined at 14, 35, 113, and 298 K in reaction center protein from Rhodobacter sphaeroides R-26 in which the native Q{sub A}, UQ{sub 10}, was removed and activity reconstituted with 22 other quinones. The majority of these had in situ midpoints lower than that of UQ{sub 10}, diminishing the {minus}{Delta}G{degree} for Q{sub A} reduction. The electron-transfer rate was determined from measurement of the quantum yield of (BChl){sub 2}{sup {sm bullet}+}Q{sub A}{sup {sm bullet}{minus}} ({Phi}{sub Q}). At 295 K, {Phi}{sub Q} was obtained from excitation-flash saturation measurements, monitoring (BChl){sub 2}{sup {sm bullet}+}Q{sub A}{sup {sm bullet}{minus}} formation optically. Between 14 and 113 K, {Phi}{sub Q} was determined from the amount of (BChl){sub 2}{sup {sm bullet}+}Q{sub A}{sup {sm bullet}{minus}}, measured by EPR, produced by excitation with a subsaturating flash. When the {minus}{Delta}G{degree} for the reduction of Q{sub A} by BPh{sup {sm bullet}{minus}} was diminished by as much as 150 meV, relative to that found in the native protein, {Phi}{sub Q} remained {>=} 0.9. However, as the exothermicity was decreased further, {Phi}{sub Q} diminished steeply. Thus, much of the 650 meV reaction {minus} {Delta}G{degree} found in the native RC is required to maintain a near-unity quantum yield. Calculation of the rate of electron transfer from BPh{sup {sm bullet}{minus}} to Q{sub A} shows the reaction slows with decreasing exothermicity. However, over the range of {minus}{Delta}G{degree} studied, the rate changed little as the system was cooled from 295 to 14 K. These results were analyzed with the model of electron transfer as a nonadiabatic, multiphoton, nonradiative decay process.

• DOE Contract Number: AC02-80ER10590
• OSTI ID: 5132065
• Journal Information: Journal of the American Chemical Society; (USA), Vol. 111:9; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
PHYTOCHROMES
ELECTRON TRANSFER
FREE ENTHALPY
QUINONES
BACTERIA
CHEMICAL REACTION KINETICS
EXPERIMENTAL DATA
LOW TEMPERATURE
MEDIUM TEMPERATURE
QUANTUM EFFICIENCY
TEMPERATURE DEPENDENCE
THERMODYNAMICS
VERY LOW TEMPERATURE
AROMATICS
DATA
EFFICIENCY
ENERGY
INFORMATION
KINETICS
MICROORGANISMS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PIGMENTS
PROTEINS
REACTION KINETICS
THERMODYNAMIC PROPERTIES
140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)