title: Spectral Hole Burning in Cyanobacterial Photosystem I with P700 in Oxidized and Neutral States.
abstract: We explored the rich satellite hole structures emerging as a result of spectral hole burning in cyanobacterial photosystem I (PSI) and demonstrated that hole burning properties of PSI, particularly at high resolution, are strongly affected by the oxidation state of the primary donor P700, as P700+effectively quenches the excitations of the lowest-energy antenna states responsible for fluorescence. Obtaining better control of this variable will be crucial for high-resolution ensemble experiments on protein energy landscapes in PSI. The separate nonphotochemical spectral hole burning (NPHB) signatures of various red antenna states were obtained, allowing for additional constraints on excitonic structure-based calculations. Preliminary evidence is presented for an additional red state of PSI of T. elongatus peaked at 712.6 nm, distinct from previously reported C708 and C715 states and possibly involving chlorophyll B15. Excitation at wavelengths as long as 800 nm results in charge separation at cryogenic temperatures in PSI also in Synechocystis sp. PCC 6803. Both the "P700+minus P700" holes and nonphotochemical spectral holes were subjected to thermocycling. The distribution of barriers manifesting in recovery of the "P700+minus P700" signature contains two components in sample-dependent proportions, likely reflecting the percentages of FAand FBclusters being successfully prereduced before the optical experiment. The barrier distribution for the recovery of the lower-energy nonphotochemical spectral holes resembles those observed for other pigment-protein complexes, suggesting similar structural elements are responsible for NPHB. Higher-energy components exhibit evidence of "domino effects" such as shifts of certain bands persisting past the lower-energy hole recovery. Thus, conformational changes triggered by excitation of one pigment likely can affect multiple pigments in this tightly packed system.
authors.affiliation: Department of Physics, Concordia University , 7141 Sherbrooke Street West, Montreal, H4B 1R4, Quebec, Canada.
authors.forename: Nicoleta
authors.initials: N
authors.lastname: Herascu
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona, United States.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Hunter
authors.affiliation: Department of Physics, Concordia University , 7141 Sherbrooke Street West, Montreal, H4B 1R4, Quebec, Canada.
authors.forename: Golia
authors.initials: G
authors.lastname: Shafiei
authors.affiliation: Department of Physics, Concordia University , 7141 Sherbrooke Street West, Montreal, H4B 1R4, Quebec, Canada.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Najafi
authors.affiliation: Department of Chemistry, Susquehanna University , Selinsgrove, Pennsylvania, United States.
authors.forename: T Wade
authors.initials: TW
authors.lastname: Johnson
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona, United States.
authors.forename: Petra
authors.initials: P
authors.lastname: Fromme
authors.affiliation: Department of Physics, Concordia University , 7141 Sherbrooke Street West, Montreal, H4B 1R4, Quebec, Canada.
authors.forename: Valter
authors.initials: V
authors.lastname: Zazubovich