@article{oai:rose-ibadai.repo.nii.ac.jp:00010251,
 author = {KIMURA, Yukihiro / HIRANO, Yu / YU, Long Jiang / SUZUKI, Hiroaki / KOBAYASHI, Masayuki / WANG, Zheng Yu},
 issue = {283},
 journal = {The Journal of Biological Chemistry},
 month = {May},
 note = {application/pdf, 論文(Article), Thermophilic purple sulfur bacterium,
Thermochromatium tepidum, can grow at
temperatures up to 58 °C and exhibits an
unusual Qy absorption at 915 nm for the core
light-harvesting complex (LH1), about 35 nm
red-shift from those of its mesophilic
counterparts. We demonstrate in this study,
using a highly purified LH1-reaction center
complex, that the LH1 Qy transition is strongly
dependent on metal cations and Ca2+ is
involved in the unusual red-shift. Removal of
the Ca2+ resulted in formation of a species with
the LH1 Qy absorption at 880 nm, and addition
of the Ca2+ to the 880-nm species recovered the
native 915-nm form. Interchange between the
two forms is fully reversible. Based on
spectroscopic and isothermal titration
calorimetry analyses, the Ca2+-binding to the
LH1 complex was estimated to occur in a
stoichiometric ratio of Ca2+/αβ -subunit = 1:1
and the binding constant was in 105 M-1 order of
magnitude, which is comparable with those for
EF-hand Ca2+-binding proteins. Despite the
high affinity, conformational changes in the
LH1 complex upon Ca2+-binding were small
and occurred slowly with a typical time
constant of about 6 minutes. Replacement of
the Ca2+ with other metal cations caused blueshifts
of the Qy bands depending on the
property of the cations, indicating that the
binding site is highly selective. Based on the
amino acid sequences of the LH1 complex,
possible Ca2+-binding sites are proposed, which
consists of several acidic amino acid residues
near the membrane interfaces of the Cterminal
region of the α-polypeptide and the Nterminal
region of the β-polypeptide.},
 pages = {13867--13873},
 title = {Calcium Ions Are Involved in the Unusual Red-Shift of the Light-Harvesting 1 Qy Transition of the Core Complex in Thermophilic Purple Sulfur Bacterium Thermochromatium tepidum},
 year = {2008}
}