title: Photophysical properties of Prochlorococcus marinus SS120 divinyl chlorophylls and phycoerythrin in vitro and in vivo.
abstract: Prochlorococcus marinus SS120 is an ecologically important and biochemically intriguing marine cyanobacterium. In addition to divinyl chlorophylls (DV-Chls) a and b it possesses a particular form of phycoerythrin (PE), but no other phycobilins and therefore no complete phycobilisomes. Here, a spectroscopic characterisation of these DV-Chls and PE is provided. Comparison of fluorescence quantum yields, excited state lifetimes and absorption characteristics indicate similar light-harvesting properties of the DV-Chls as their monovinyl counterparts. PE, which is present only in tiny amounts, was purified and considerably enriched. A phycourobilin to phycoerythrobilin ratio of 3:1 chromophores per (alphabeta) PE monomer is suggested. The in vitro fluorescence lifetime of PE is 1.74 ns. In vivo time-resolved fluorescence measurements with synchrotron radiation were used to investigate the possible role of PE in light-harvesting. The fluorescence decay time for PE is about 550 ps, indicating an unusually slow excitation energy transfer. The decay time slowed to 1 ns after addition of glycerol to cell cultures. The contribution of PE to total light-harvesting capacity was estimated to be about one (alphabeta) PE monomer per 330 DV-Chl b molecules. Thus, the capacity of PE to function primarily as a photosynthetic light-harvesting pigment in P. marinus SS120 is low.
authors.affiliation: Institut für Biologie/Genetik, Humboldt-Universität zu Berlin, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Steglich
authors.forename: Conrad W
authors.initials: CW
authors.lastname: Mullineaux
authors.forename: Klaus
authors.initials: K
authors.lastname: Teuchner
authors.forename: Wolfgang R
authors.initials: WR
authors.lastname: Hess
authors.forename: Heiko
authors.initials: H
authors.lastname: Lokstein
mesh_terms: D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000737:chemistry*; D000458:Cyanobacteria / Q000737:chemistry*; D007700:Kinetics; D010777:Photochemistry; D045524:Phycobilisomes; D010799:Phycoerythrin / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D045524:Phycobilisomes; D010799:Phycoerythrin; D002734:Chlorophyll