title: Assignment of the low-temperature fluorescence in oxygen-evolving photosystem II.
abstract: Low-temperature absorption and fluorescence spectra of fully active cores and membrane-bound PS II preparations are compared. Detailed temperature dependence of fluorescence spectra between 5 and 70 K are presented as well as 1.7-K fluorescence line-narrowed (FLN) spectra of cores, confirming that PS II emission is composite. Spectra are compared to those reported for LHCII, CP43, CP47 and D1/D2/cytit b559 subunits of PS II. A combination of subunit spectra cannot account for emission of active PS II. The complex temperature dependence of PS II fluorescence is interpretable by noting that excitation transfer from CP43 and CP47 to the reaction centre is slow, and strongly dependent on the precise energy at which a 'slow-transfer' pigment in CP43 or CP47 is located within its inhomogeneous distribution. PS II fluorescence arises from CP43 and CP47 'slow-transfer' states, convolved by this dependence. At higher temperatures, thermally activated excitation transfer to the PS II charge-separating system bypasses such bottlenecks. As the charge-separating state of active PS II absorbs at >700 nm, PS II emission in the 680-700 nm region is unlikely to arise from reaction centre pigments. PS II emission at physiological temperatures is discussed in terms of these results.
authors.affiliation: Research School of Chemistry, Australian National University, Building 35 Science Road, Canberra, ACT 0200, Australia. krausz@rsc.anu.edu.au
authors.forename: Elmars
authors.initials: E
authors.lastname: Krausz
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Hughes
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Smith
authors.forename: Ron J
authors.initials: RJ
authors.lastname: Pace
authors.forename: Sindra Peterson
authors.initials: SP
authors.lastname: Arsköld
mesh_terms: D004735:Energy Transfer; D005453:Fluorescence; D010100:Oxygen / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism*; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature
chemical_list: D045332:Photosystem II Protein Complex; D010100:Oxygen