Structure of a Histidine Ligand in the Photosynthetic Oxygen-Evolving Complex As Studied by Light-Induced Fourier Transform Infrared Difference Spectroscopy
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- 作者：Takumi Noguchi ; Yorinao Inoue ; and Xiao-Song Tang
- 刊名：Biochemistry
- 出版年：1999
- 出版时间：August 3, 1999
- 年：1999
- 卷：38
- 期：31
- 页码：10187 - 10195
- 全文大小：106K
- 年卷期：v.38,no.31(August 3, 1999)
- ISSN：1520-4995
文摘
Fourier transform infrared (FTIR) signals of a histidine side chain were identified in flash-induced S2/S1 difference spectra of the oxygen-evolving complex (OEC) of photosystem II (PS II) usingPS II membranes from globally 15N-labeled spinach and PS II core complexes from Synechocystis cellsin which both the imidazole nitrogens of histidine were selectively labeled with 15N. A negative band at1113-1114 cm-1 was downshifted by 7 cm-1 upon both global 15N-labeling and selective [15N]His labeling,and assigned to the C-N stretching mode of the imidazole ring. This band was unaffected by H-Dexchange in the PS II preparations. In addition, several peaks observed at 2500-2850 cm-1 all downshiftedupon global and selective 15N-labeling. These were ascribed to Fermi resonance peaks on a hydrogen-bonding N-H stretching band of the histidine side chain. FTIR measurements of model compounds ofthe histidine side chain showed that the C-N stretching band around 1100 cm-1 can be a useful IRmarker of the protonation form of the imidazole ring. The band appeared with frequencies in the followingorder: N
-protonated (>1100 cm-1) > imidazolate > imidazolium > N
-protonated (<1095 cm-1). Thefrequency shift upon N-deuteration was occurred in the following order: imidazolium (15-20 cm-1) >N-protonated (5-10 cm-1) > N-protonated 
imidazolate (~0 cm-1). On the basis of these findingstogether with the Fermi resonance peaks at >2500 cm-1 as a marker of N-H hydrogen-bonding, weconcluded that the histidine residue in the S2/S1 spectrum is protonated at the N site and that this N-His hydrogen bonded. This histidine side chain probably ligated the redox-active Mn ion at the N site, andthus, oxidation of the Mn cluster upon S2 formation perturbed the histidine vibrations, causing this histidineto appear in the S2/S1 difference spectrum.
-protonated (>1100 cm-1) > imidazolate > imidazolium > N-protonated (<1095 cm-1). Thefrequency shift upon N-deuteration was occurred in the following order: imidazolium (15-20 cm-1) >N-protonated (5-10 cm-1) > N-protonated imidazolate (~0 cm-1). On the basis of these findingstogether with the Fermi resonance peaks at >2500 cm-1 as a marker of N-H hydrogen-bonding, weconcluded that the histidine residue in the S2/S1 spectrum is protonated at the N site and that this N-His hydrogen bonded. This histidine side chain probably ligated the redox-active Mn ion at the N site, andthus, oxidation of the Mn cluster upon S2 formation perturbed the histidine vibrations, causing this histidineto appear in the S2/S1 difference spectrum.