Electronic spectra of PS I mutants: the peripheral subunits do not bind red chlorophylls in Synechocystis sp. PCC 6803.
Steady-state fluorescence and absorption spectra have been obtained in the Qy spectral region (690-780 nm and 600-750 nm, respectively) for several subunit-deficient photosystem I mutants from the cyanobacterium Synechocystis sp. PCC 6803. The 77 K fluorescence spectra of the wild-type and subunit-deficient mutant photosystem I particles are all very similar, peaking at approximately 720 nm with essentially the same excitation spectrum. Because emission from far-red chlorophylls absorbing near 708 nm dominates low-temperature fluorescence in Synechocystis sp., these pigments are not coordinated to any the subunits PsaF, Psa I, PsaJ, PsaK, PsaL, or psaM. The room temperature (wild-type-mutant) absorption difference spectra for trimeric mutants lacking the PsaF/J, PsaK, and PsaM subunits suggest that these mutants are deficient in core antenna chlorophylls (Chls) absorbing near 685, 670, 675, and 700 nm, respectively. The absorption difference spectrum for the PsaF/J/I/L-deficient photosystem I complexes at 5 K reveals considerably more structure than the room-temperature spectrum. The integrated absorbance difference spectra (when normalized to the total PS I Qy spectral area) are comparable to the fractions of Chls bound by the respective (groups of) subunits, according to the 4-A density map of PS I from Synechococcus elongatus. The spectrum of the monomeric PsaL-deficient mutant suggests that this subunit may bind pigments absorbing near 700 nm.
Soukoulis
V
V
Ames Laboratory, U.S. Department of Energy, and Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
Savikhin
S
S
Xu
W
W
Chitnis
P R
PR
Struve
W S
WS
D002734:Chlorophyll / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D000458:Cyanobacteria / Q000737:chemistry* / Q000235:genetics*; D009154:Mutation; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry
D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll