17 research outputs found
Weak temperature dependence of P (+) H A (-) recombination in mutant Rhodobacter sphaeroides reaction centers
International audienceIn contrast with findings on the wild-type Rhodobacter sphaeroides reaction center, biexponential P (+) H A (-) → PH A charge recombination is shown to be weakly dependent on temperature between 78 and 298 K in three variants with single amino acids exchanged in the vicinity of primary electron acceptors. These mutated reaction centers have diverse overall kinetics of charge recombination, spanning an average lifetime from ~2 to ~20 ns. Despite these differences a protein relaxation model applied previously to wild-type reaction centers was successfully used to relate the observed kinetics to the temporal evolution of the free energy level of the state P (+) H A (-) relative to P (+) B A (-) . We conclude that the observed variety in the kinetics of charge recombination, together with their weak temperature dependence, is caused by a combination of factors that are each affected to a different extent by the point mutations in a particular mutant complex. These are as follows: (1) the initial free energy gap between the states P (+) B A (-) and P (+) H A (-) , (2) the intrinsic rate of P (+) B A (-) → PB A charge recombination, and (3) the rate of protein relaxation in response to the appearance of the charge separated states. In the case of a mutant which displays rapid P (+) H A (-) recombination (ELL), most of this recombination occurs in an unrelaxed protein in which P (+) B A (-) and P (+) H A (-) are almost isoenergetic. In contrast, in a mutant in which P (+) H A (-) recombination is relatively slow (GML), most of the recombination occurs in a relaxed protein in which P (+) H A (-) is much lower in energy than P (+) H A (-) . The weak temperature dependence in the ELL reaction center and a YLH mutant was modeled in two ways: (1) by assuming that the initial P (+) B A (-) and P (+) H A (-) states in an unrelaxed protein are isoenergetic, whereas the final free energy gap between these states following the protein relaxation is large (~250 meV or more), independent of temperature and (2) by assuming that the initial and final free energy gaps between P (+) B A (-) and P (+) H A (-) are moderate and temperature dependent. In the case of the GML mutant, it was concluded that the free energy gap between P (+) B A (-) and P (+) H A (-) is large at all times
Thermodynamics of the Primary Electron Transfer Reaction in D1/D2 Cytochrome B-559 Reaction Centres
Mutations that Affect the Donor Midpoint Potential in Reaction Centers from Rhodobacter Sphaeroides
Model Calculations on the Fluorescence Kinetics of Isolated Bacterial Reaction Centers from Rhodobacter sphaeroides
Electrostatic Effects on the Speed and Directionality of Electron Transfer in Bacterial Reaction Centers: The Special Role of Tyrosine M-208
Energy Transfer and Charge Separation Kinetics in the Reaction Center of Chloroflexus aurantiacus Studied by Picosecond Time-Resolved Fluorescence Spectroscopy
Weak temperature dependence of P + H A − recombination in mutant Rhodobacter sphaeroides reaction centers
Some Recent Developments in Electron Transfer: Charge Separation, Long Distances, Solvent Dynamics, and Free Energy Aspects
Several topics in electron transfers are discussed, including the charge separation in a bacterial photosynthetic reaction center, long range electron transfers, solvent dynamical effects in electron transfer, and free energy aspects of these reactions