title: Two equilibration pools of chlorophylls in the Photosystem I core antenna of Chlamydomonas reinhardtii.
abstract: Femtosecond transient absorption spectroscopy was applied for a comparative study of excitation decay in several different Photosystem I (PSI) core preparations from the green alga Chlamydomonas reinhardtii. For PSI cores with a fully interconnected network of chlorophylls, the excitation energy was equilibrated over a pool of chlorophylls absorbing at approximately 683 nm, independent of excitation wavelength [Gibasiewicz et al. J Phys Chem B 105:11498-11506, 2001; J Phys Chem B 106:6322-6330, 2002]. In preparations with impaired connectivity between chlorophylls, we have found that the spectrum of chlorophylls connected to the reaction center (i.e., with approximately 20 ps decay time) over which the excitation is equilibrated becomes excitation-wavelength-dependent. Excitation at 670 nm is finally equilibrated over chlorophylls absorbing at approximately 675 nm, whereas excitation at 695 nm or 700 nm is equilibrated over chlorophylls absorbing at approximately 683 nm. This indicates that in the vicinity of the reaction center there are two spectrally different and spatially separated pools of chlorophylls that are equally capable of effective excitation energy transfer to the reaction center. We propose that they are related to the two groups of central PSI core chlorophylls lying on the opposite sides of reaction center.
authors.affiliation: School of Life Sciences, Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, AZ 85287-4501, USA. krzyszgi@amu.edu.pl
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Gibasiewicz
authors.forename: V M
authors.initials: VM
authors.lastname: Ramesh
authors.forename: Su
authors.initials: S
authors.lastname: Lin
authors.forename: Kevin
authors.initials: K
authors.lastname: Redding
authors.forename: Neal W
authors.initials: NW
authors.lastname: Woodbury
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Webber
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000502:physiology*; D002734:Chlorophyll / Q000378:metabolism*; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D045331:Photosystem I Protein Complex; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D002734:Chlorophyll