TY - JOUR
T1 - Excitation energy transfer in thylakoid membranes from Chlamydomonas reinhardtii lacking chlorophyll b and with mutant Photosystem I
AU - Melkozernov, Alexander N.
AU - Su, Hui
AU - Webber, Andrew
AU - Blankenship, Robert E.
N1 - Funding Information:
We thank Dr J. Guikema for the PsaA/B antisera. This work was supported by NSF grant MCB 9418415 to R.E.B. and the National Research Initiatives Competitive Grants Program, grant 95373062044 to A.N.W. This is publication #344 of the Center for the Study of Early Events in Photosynthesis at Arizona State University.
PY - 1998
Y1 - 1998
N2 - Energy trapping in Photosystem I (PS I) was studied by time-resolved fluorescence spectroscopy of PS II-deleted Chl b-minus thylakoid membranes isolated from site-directed mutants of Chlamydomonas reinhardtii with specific amino acid substitutions of a histidine ligand to P700. In vivo the fluorescence of the PS I core antenna in mutant thylakoids with His-656 of PsaB replaced by asparagine, serine or phenylalanine is characterized by an increase in the lifetime of the fast decay component ascribed to the energy trapping in PS I (25 ps in wild type PS I with intact histidine-656, 50 ps in the mutant PS I with asparagine-656 and 70 ps in the mutant PS I with phenylalanine-656). Assuming that the excitation dynamics in th PS I antenna are trap-limited, the increase in the trapping time suggests a decrease in the primary charge separation rate. Western blot analysis showed that the mutants accumulate significantly less PS I than wild type. Spectroscopically, the mutations lead to a decrease in relative quantum yield of the trapping in the PS I core and increase in relative quantum yield of the fluorescence decay phase ascribed to uncoupled chlorophyll-protein complexes which suggests that improper assembly of PS I and LHC in the mutant thylakoids may result in energy uncoupling in PS I.
AB - Energy trapping in Photosystem I (PS I) was studied by time-resolved fluorescence spectroscopy of PS II-deleted Chl b-minus thylakoid membranes isolated from site-directed mutants of Chlamydomonas reinhardtii with specific amino acid substitutions of a histidine ligand to P700. In vivo the fluorescence of the PS I core antenna in mutant thylakoids with His-656 of PsaB replaced by asparagine, serine or phenylalanine is characterized by an increase in the lifetime of the fast decay component ascribed to the energy trapping in PS I (25 ps in wild type PS I with intact histidine-656, 50 ps in the mutant PS I with asparagine-656 and 70 ps in the mutant PS I with phenylalanine-656). Assuming that the excitation dynamics in th PS I antenna are trap-limited, the increase in the trapping time suggests a decrease in the primary charge separation rate. Western blot analysis showed that the mutants accumulate significantly less PS I than wild type. Spectroscopically, the mutations lead to a decrease in relative quantum yield of the trapping in the PS I core and increase in relative quantum yield of the fluorescence decay phase ascribed to uncoupled chlorophyll-protein complexes which suggests that improper assembly of PS I and LHC in the mutant thylakoids may result in energy uncoupling in PS I.
KW - Energy transfer kinetics
KW - Energy uncoupling
KW - P
KW - Photosystem I (Chlamydomonas reinhardtii)
KW - Site-directed mutants
KW - Thylakoids
KW - Time-resolved fluorescence
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U2 - 10.1023/A:1006016631150
DO - 10.1023/A:1006016631150
M3 - Article
AN - SCOPUS:0031823277
SN - 0166-8595
VL - 56
SP - 197
EP - 207
JO - Photosynthesis research
JF - Photosynthesis research
IS - 2
ER -