title: Photo-accumulation of the P+QB- radical pair state in purple bacterial reaction centres that lack the QA ubiquinone.
abstract: 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.
authors.affiliation: Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK.
authors.forename: Marion C
authors.initials: MC
authors.lastname: Wakeham
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Goodwin
authors.forename: Craig
authors.initials: C
authors.lastname: McKibbin
authors.forename: Michael R
authors.initials: MR
authors.lastname: Jones
mesh_terms: D005609:Free Radicals; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D011199:Potentiometry; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D014451:Ubiquinone / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D045322:Photosynthetic Reaction Center Complex Proteins; D014451:Ubiquinone