Changes of low-frequency vibrational modes induced by universal 15N- and 13C-isotope labeling in S2/S1 FTIR difference spectrum of oxygen-evolving complex.
The effects of universal (15)N- and (13)C-isotope labeling on the low- (650-350 cm(-1)) and mid-frequency (1800-1200 cm(-1)) S(2)/S(1) Fourier transform infrared (FTIR) difference spectrum of the photosynthetic oxygen-evolving complex (OEC) were investigated in histidine-tagged photosystem (PS) II core particles from Synechocystis sp. PCC 6803. In the mid-frequency region, the amide II modes were predominantly affected by (15)N-labeling, whereas, in addition to the amide II, the amide I and carboxylate modes were markedly affected by (13)C-labeling. In the low-frequency region, by comparing a light-induced spectrum in the presence of ferricyanide as the electron acceptor, with the double difference S(2)/S(1) spectrum obtained by subtracting the Q(A)(-)/Q(A) from the S(2)Q(A)(-)/S(1)Q(A) spectrum, considerable numbers of bands found in the light-induced spectrum were assigned to the S(2)/S(1) vibrational modes in the unlabeled PS II core particles. Upon (13)C-labeling, changes were observed for most of the prominent bands in the S(2)/S(1) spectrum. Although (15)N-labeling also induced changes similar to those by (13)C-labeling, the bands at 616(-), 605(+), 561(+), 555(-), and 544(-) cm(-1) were scarcely affected by (15)N-labeling. These results indicated that most of the vibrational modes found in the low-frequency spectrum are derived from the coupling between the Mn-cluster and groups containing nitrogen and/or carbon atom(s) in a direct manner and/or through hydrogen bonding. Interestingly, an intensive band at 577(-) cm(-1) was not affected by (15)N- and (13)C-isotope labeling, indicating that this band arises from the mode that does not include either nitrogen or carbon atoms, such as the skeletal vibration of the Mn-cluster or stretching vibrational modes of the Mn-ligand.
Kimura
Yukihiro
Y
Laboratory for Photo-Biology (1), RIKEN Photodynamics Research Center, Institute of Physical and Chemical Research, 519-1399 Aoba, Aramaki, Aoba, Sendai 980-0845, Japan. ykimura@postman.riken.go.jp
Mizusawa
Naoki
N
Ishii
Asako
A
Yamanari
Toshihiro
T
Ono
Taka-aki
TA
D002247:Carbon Isotopes / Q000378:metabolism; D000458:Cyanobacteria / Q000737:chemistry; D005292:Ferricyanides / Q000737:chemistry; D008027:Light; D008345:Manganese / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D010103:Oxygen Isotopes / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
D002247:Carbon Isotopes; D005292:Ferricyanides; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D045332:Photosystem II Protein Complex; C007931:hexacyanoferrate III; D008345:Manganese; D010100:Oxygen