A native electrostatic environment near Q(B) is not sufficient to ensure rapid proton delivery in photosynthetic reaction centers.
Flash-induced absorption spectroscopy has been used to characterize Rhodobacter capsulatus reaction centers mutated in the secondary quinone acceptor site (Q(B). We compared the wild-type, the L212Glu-L213Asp --> Ala-Ala photosynthetically incompetent double mutant (DM), and two photocompetent revertants, the DM+L217Arg --> Cys and the DM+M5Asn- --> Asp strains. The electrostatic environment for Q(B)- is different in the two revertant strains. Only the L217Arg --> Cys mutation nearly restores the native electrostatic environment of Q(B)-. However, the level of recovery of the reaction center function, measured by the rates of second electron transfer and cytochrome c turnover, is quite incomplete in both strains. This shows that a wild-type-like electrostatic environment of Q(B)- cannot ensure on its own, rapid and efficient proton transfer to Q(B)-.
Valerio-Lepiniec
M
M
Centre de Génétique Moléculaire, CNRS, Gif/Yvette, France.
Delcroix
J D
JD
Schiffer
M
M
Hanson
D K
DK
Sebban
P
P
D003574:Cytochrome c Group / Q000378:metabolism; D004579:Electron Transport; D008027:Light; D009154:Mutation; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000502:physiology*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D011522:Protons; D011809:Quinones / Q000378:metabolism*; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000378:metabolism*; D013053:Spectrophotometry; D055672:Static Electricity; D013816:Thermodynamics
D003574:Cytochrome c Group; D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons; D011809:Quinones