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Photo‐accumulation of the P + Q B − radical pair state in purple bacterial reaction centres that lack the Q A ubiquinone
Author(s) -
Wakeham Marion C,
Goodwin Matthew G,
McKibbin Craig,
Jones Michael R
Publication year - 2003
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(03)00270-9
Subject(s) - rhodobacter sphaeroides , protonation , electron transfer , chemistry , photosynthetic reaction centre , photochemistry , stereochemistry , cofactor , electron transport chain , yield (engineering) , crystallography , ion , photosynthesis , biochemistry , physics , enzyme , organic chemistry , thermodynamics
Photo‐excitation of membrane‐bound Rhodobacter sphaeroides reaction centres containing the mutation Ala M260 to Trp (AM260W) resulted in the accumulation of a radical pair state involving the photo‐oxidised primary electron donor (P). This state had a lifetime of hundreds of milliseconds and its formation was inhibited by stigmatellin. The absence of the Q A ubiquinone in the AM260W reaction centre suggests that this long‐lived radical pair state is P + Q B − , although the exact reduction/protonation state of the Q B quinone remains to be confirmed. The blockage of active branch (A‐branch) electron transfer by the AM260W mutation implies that this P + Q B − state is formed by electron transfer along the so‐called inactive branch (B‐branch) of reaction centre cofactors. We discuss how further mutations may affect the yield of the P + Q B − state, including a double alanine mutation (EL212A/DL213A) that probably has a direct effect on the efficiency of the low yield electron transfer step from the anion of the B‐branch bacteriopheophytin (H B − ) to the Q B ubiquinone.