TY - JOUR
T1 - Spectral and kinetic analysis of the energy coupling in the PS I-LHC I supercomplex from the green alga Chlamydomonas reinhardtii at 77 K
AU - Melkozernov, Alexander N.
AU - Kargul, Joanna
AU - Lin, Su
AU - Barber, James
AU - Blankenship, Robert E.
N1 - Funding Information:
The work was supported by an NRI/CSREES/ USDA Grant 2003-35318-13665 to ANM, an NSF grant MCB 0091250 to REB, and a BBSRC grant to J.B. and J.K. This is publication # 601 of the Center for the Study of Early Events in Photosynthesis at ASU.
PY - 2005/11
Y1 - 2005/11
N2 - Energy transfer processes in the chlorophyll antenna of the PS I-LHCI supercomplexes from the green alga Chlamydomonas reinhardtii have been studied at 77 K using transient absorption spectroscopy with multicolor excitation in the 640-670 nm region. Comparison of the kinetic data obtained at low and room temperatures indicates that the slow ∼100 ps excitation equilibration phase that is characteristic of energy coupling of the LHCI peripheral antenna to the PS I core at physiological temperatures (Melkozernov AN, Kargul J, Lin S, Barber J and Blankenship RE (2004) J Phys Chem B 108: 10547-10555) is not observed in the excitation dynamics of the PS I-LHCI supercomplex at 77 K. This suggests that at low temperatures the peripheral antenna is energetically uncoupled from the PS I core antenna. Under these conditions the observed kinetic phases on the time scales from subpicoseconds to tens of picoseconds represent the superposition of the processes occurring independently in the PS I core antenna and the Chl a/b containing LHCI antenna. In the PS I-LHCI supercomplex with two uncoupled antennas the excitation is channeled to the excitation sinks formed at low temperature by clusters of red pigments. A better spectral resolution of the transient absorption spectra at 77 K results in detection of two ΔA bands originating from the rise of photobleaching on the picosecond time scale of two clearly distinguished pools of low energy absorbing Chls in the PS I-LHCI supercomplex. The first pool of low energy pigments absorbing at 687 nm is likely to originate from the red pigments in the LHCI where the Lhca1 protein is most abundant. The second pool at 697 nm is suggested to result either from the structural interaction of the LHCI and the PS I core or from other Lhca proteins in the antenna. The kinetic data are discussed based on recent structural models of the PS I-LHCI. It is proposed that the uncoupling of pigment pools may be a control mechanism that regulates energy flow in Photosystem I.
AB - Energy transfer processes in the chlorophyll antenna of the PS I-LHCI supercomplexes from the green alga Chlamydomonas reinhardtii have been studied at 77 K using transient absorption spectroscopy with multicolor excitation in the 640-670 nm region. Comparison of the kinetic data obtained at low and room temperatures indicates that the slow ∼100 ps excitation equilibration phase that is characteristic of energy coupling of the LHCI peripheral antenna to the PS I core at physiological temperatures (Melkozernov AN, Kargul J, Lin S, Barber J and Blankenship RE (2004) J Phys Chem B 108: 10547-10555) is not observed in the excitation dynamics of the PS I-LHCI supercomplex at 77 K. This suggests that at low temperatures the peripheral antenna is energetically uncoupled from the PS I core antenna. Under these conditions the observed kinetic phases on the time scales from subpicoseconds to tens of picoseconds represent the superposition of the processes occurring independently in the PS I core antenna and the Chl a/b containing LHCI antenna. In the PS I-LHCI supercomplex with two uncoupled antennas the excitation is channeled to the excitation sinks formed at low temperature by clusters of red pigments. A better spectral resolution of the transient absorption spectra at 77 K results in detection of two ΔA bands originating from the rise of photobleaching on the picosecond time scale of two clearly distinguished pools of low energy absorbing Chls in the PS I-LHCI supercomplex. The first pool of low energy pigments absorbing at 687 nm is likely to originate from the red pigments in the LHCI where the Lhca1 protein is most abundant. The second pool at 697 nm is suggested to result either from the structural interaction of the LHCI and the PS I core or from other Lhca proteins in the antenna. The kinetic data are discussed based on recent structural models of the PS I-LHCI. It is proposed that the uncoupling of pigment pools may be a control mechanism that regulates energy flow in Photosystem I.
KW - Core antenna
KW - Excited state dynamics
KW - Green algae
KW - LHCI peripheral antenna
KW - Nonphotochemical trapping
KW - PS I-LHCI supercomplex
KW - Photochemical trapping
KW - Photosynthesis
KW - Photosystem I
KW - Red pigments
KW - Transient absorption spectroscopy
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U2 - 10.1007/s11120-005-4118-z
DO - 10.1007/s11120-005-4118-z
M3 - Article
C2 - 16172939
AN - SCOPUS:25444443883
SN - 0166-8595
VL - 86
SP - 203
EP - 216
JO - Photosynthesis research
JF - Photosynthesis research
IS - 1-2
ER -